diff --git a/index.html b/index.html
index 5e3380f..1e768f2 100644
--- a/index.html
+++ b/index.html
@@ -11,6 +11,9 @@
         margin-right: -1px;
         animation: blink 1s step-end infinite;
     }
+    .selection {
+        background-color: #b3d7ff;
+    }
     @keyframes blink {
         50% {
             border-color: transparent;
diff --git a/input.js b/input.js
deleted file mode 100644
index 056b1f0..0000000
--- a/input.js
+++ /dev/null
@@ -1,71 +0,0 @@
-export function setupInput(buffer, cursor, onChange) {
-  document.addEventListener("keydown", (e) => {
-    if (e.key === "ArrowUp") {
-      e.preventDefault();
-      if (cursor.line > 0) cursor.line--;
-      cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
-      onChange();
-      return;
-    }
-    if (e.key === "ArrowDown") {
-      e.preventDefault();
-      if (cursor.line < buffer.length - 1) cursor.line++;
-      cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
-      onChange();
-      return;
-    }
-    if (e.key === "ArrowLeft") {
-      e.preventDefault();
-      if (cursor.col > 0) cursor.col--;
-      else if (cursor.line > 0) {
-        cursor.line--;
-        cursor.col = buffer[cursor.line].length;
-      }
-      onChange();
-      return;
-    }
-    if (e.key === "ArrowRight") {
-      e.preventDefault();
-      if (cursor.col < buffer[cursor.line].length) cursor.col++;
-      else if (cursor.line < buffer.length - 1) {
-        cursor.line++;
-        cursor.col = 0;
-      }
-      onChange();
-      return;
-    }
-    if (e.key === "Backspace") {
-      e.preventDefault();
-      if (cursor.col > 0) {
-        const line = buffer[cursor.line];
-        buffer[cursor.line] = line.slice(0, cursor.col - 1) + line.slice(cursor.col);
-        cursor.col--;
-      } else if (cursor.line > 0) {
-        cursor.col = buffer[cursor.line - 1].length;
-        buffer[cursor.line - 1] += buffer[cursor.line];
-        buffer.splice(cursor.line, 1);
-        cursor.line--;
-      }
-      onChange();
-      return;
-    }
-    if (e.key === "Enter") {
-      e.preventDefault();
-      const line = buffer[cursor.line];
-      const rest = line.slice(cursor.col);
-      buffer[cursor.line] = line.slice(0, cursor.col);
-      buffer.splice(cursor.line + 1, 0, rest);
-      cursor.line++;
-      cursor.col = 0;
-      onChange();
-      return;
-    }
-    if (e.key.length === 1) {
-      e.preventDefault();
-      const line = buffer[cursor.line];
-      buffer[cursor.line] = line.slice(0, cursor.col) + e.key + line.slice(cursor.col);
-      cursor.col++;
-      onChange();
-    }
-  });
-}
diff --git a/lib/cursor.js b/lib/cursor.js
new file mode 100644
index 0000000..6a322e1
--- /dev/null
+++ b/lib/cursor.js
@@ -0,0 +1,25 @@
+export function moveUp(buffer, cursor) {
+  if (cursor.line > 0) cursor.line--;
+  cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
+}
+
+export function moveDown(buffer, cursor) {
+  if (cursor.line < buffer.length - 1) cursor.line++;
+  cursor.col = Math.min(cursor.col, buffer[cursor.line].length);
+}
+
+export function moveLeft(buffer, cursor) {
+  if (cursor.col > 0) cursor.col--;
+  else if (cursor.line > 0) {
+    cursor.line--;
+    cursor.col = buffer[cursor.line].length;
+  }
+}
+
+export function moveRight(buffer, cursor) {
+  if (cursor.col < buffer[cursor.line].length) cursor.col++;
+  else if (cursor.line < buffer.length - 1) {
+    cursor.line++;
+    cursor.col = 0;
+  }
+}
diff --git a/lib/html.js b/lib/html.js
new file mode 100644
index 0000000..96673e4
--- /dev/null
+++ b/lib/html.js
@@ -0,0 +1,10 @@
+export function escapeChar(c) {
+  if (c === "&") return "&amp;";
+  if (c === "<") return "&lt;";
+  if (c === ">") return "&gt;";
+  return c;
+}
+
+export function escapeHtml(s) {
+  return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
+}
diff --git a/lib/keyboard.js b/lib/keyboard.js
new file mode 100644
index 0000000..7087da6
--- /dev/null
+++ b/lib/keyboard.js
@@ -0,0 +1,215 @@
+import { moveUp, moveDown, moveLeft, moveRight } from "./cursor.js";
+import { hasSelection, selectedRange, clearSelection, deleteSelection } from "./selection.js";
+import { elementToPos } from "./mouse.js";
+
+export function setupInput(buffer, cursor, selection, onChange) {
+  let isMouseDown = false;
+
+  function startDrag(e) {
+    if (!e.target.closest("#text")) return;
+    isMouseDown = true;
+    const pos = elementToPos(e.clientX, e.clientY, buffer);
+    cursor.line = pos.line;
+    cursor.col = pos.col;
+    selection.anchor = { ...pos };
+    selection.head = { ...pos };
+    onChange();
+  }
+
+  function drag(e) {
+    if (!isMouseDown) return;
+    const pos = elementToPos(e.clientX, e.clientY, buffer);
+    cursor.line = pos.line;
+    cursor.col = pos.col;
+    selection.head = { ...pos };
+    onChange();
+  }
+
+  function endDrag() {
+    isMouseDown = false;
+  }
+
+  function selectWord(e) {
+    if (!e.target.closest("#text")) return;
+    const pos = elementToPos(e.clientX, e.clientY, buffer);
+    const line = buffer[pos.line];
+    let start = pos.col;
+    let end = pos.col;
+    while (start > 0 && /\w/.test(line[start - 1])) start--;
+    while (end < line.length && /\w/.test(line[end])) end++;
+    cursor.line = pos.line;
+    cursor.col = end;
+    selection.anchor = { line: pos.line, col: start };
+    selection.head = { line: pos.line, col: end };
+    onChange();
+  }
+
+  function moveCursor(newLine, newCol, extending) {
+    if (extending) {
+      if (selection.anchor === null)
+        selection.anchor = { line: cursor.line, col: cursor.col };
+      selection.head = { line: newLine, col: newCol };
+    } else {
+      clearSelection(selection);
+    }
+    cursor.line = newLine;
+    cursor.col = newCol;
+  }
+
+  function getSelectedText() {
+    const range = selectedRange(selection);
+    if (!range) return "";
+    const { start, end } = range;
+    if (start.line === end.line)
+      return buffer[start.line].slice(start.col, end.col);
+    const lines = [buffer[start.line].slice(start.col)];
+    for (let i = start.line + 1; i < end.line; i++)
+      lines.push(buffer[i]);
+    lines.push(buffer[end.line].slice(0, end.col));
+    return lines.join("\n");
+  }
+
+  function insertText(text) {
+    if (hasSelection(selection)) deleteSelection(buffer, cursor, selection);
+    const pasteLines = text.split("\n");
+    const line = buffer[cursor.line];
+    const before = line.slice(0, cursor.col);
+    const after = line.slice(cursor.col);
+    buffer[cursor.line] = before + pasteLines[0] + after;
+    for (let i = 1; i < pasteLines.length; i++)
+      buffer.splice(cursor.line + i, 0, pasteLines[i]);
+    cursor.line += pasteLines.length - 1;
+    cursor.col = pasteLines[pasteLines.length - 1].length +
+      (pasteLines.length === 1 ? before.length : 0);
+    clearSelection(selection);
+  }
+
+  function selectAll() {
+    selection.anchor = { line: 0, col: 0 };
+    selection.head = { line: buffer.length - 1, col: buffer[buffer.length - 1].length };
+    cursor.line = buffer.length - 1;
+    cursor.col = buffer[buffer.length - 1].length;
+  }
+
+  document.addEventListener("mousedown", startDrag);
+  document.addEventListener("mousemove", drag);
+  document.addEventListener("mouseup", endDrag);
+  document.addEventListener("dblclick", selectWord);
+
+  document.addEventListener("paste", (e) => {
+    e.preventDefault();
+    const text = e.clipboardData.getData("text");
+    if (!text) return;
+    insertText(text);
+    onChange();
+  });
+
+  document.addEventListener("keydown", (e) => {
+    const mod = e.ctrlKey || e.metaKey;
+    const extending = e.shiftKey;
+
+    if (mod) {
+      if (e.key === "c") {
+        e.preventDefault();
+        const text = getSelectedText();
+        if (text) navigator.clipboard.writeText(text);
+        return;
+      }
+      if (e.key === "x") {
+        e.preventDefault();
+        const text = getSelectedText();
+        if (text) navigator.clipboard.writeText(text);
+        deleteSelection(buffer, cursor, selection);
+        onChange();
+        return;
+      }
+      if (e.key === "v") {
+        return;
+      }
+      if (e.key === "a") {
+        e.preventDefault();
+        selectAll();
+        onChange();
+        return;
+      }
+      return;
+    }
+
+    if (e.key === "ArrowUp") {
+      e.preventDefault();
+      const newLine = Math.max(0, cursor.line - 1);
+      const newCol = Math.min(cursor.col, buffer[newLine].length);
+      moveCursor(newLine, newCol, extending);
+      onChange();
+      return;
+    }
+    if (e.key === "ArrowDown") {
+      e.preventDefault();
+      const newLine = Math.min(buffer.length - 1, cursor.line + 1);
+      const newCol = Math.min(cursor.col, buffer[newLine].length);
+      moveCursor(newLine, newCol, extending);
+      onChange();
+      return;
+    }
+    if (e.key === "ArrowLeft") {
+      e.preventDefault();
+      let newLine = cursor.line;
+      let newCol = cursor.col;
+      if (newCol > 0) newCol--;
+      else if (newLine > 0) { newLine--; newCol = buffer[newLine].length; }
+      moveCursor(newLine, newCol, extending);
+      onChange();
+      return;
+    }
+    if (e.key === "ArrowRight") {
+      e.preventDefault();
+      let newLine = cursor.line;
+      let newCol = cursor.col;
+      if (newCol < buffer[cursor.line].length) newCol++;
+      else if (newLine < buffer.length - 1) { newLine++; newCol = 0; }
+      moveCursor(newLine, newCol, extending);
+      onChange();
+      return;
+    }
+    if (e.key === "Backspace") {
+      e.preventDefault();
+      if (hasSelection(selection)) {
+        deleteSelection(buffer, cursor, selection);
+      } else if (cursor.col > 0) {
+        const line = buffer[cursor.line];
+        buffer[cursor.line] = line.slice(0, cursor.col - 1) + line.slice(cursor.col);
+        cursor.col--;
+      } else if (cursor.line > 0) {
+        cursor.col = buffer[cursor.line - 1].length;
+        buffer[cursor.line - 1] += buffer[cursor.line];
+        buffer.splice(cursor.line, 1);
+        cursor.line--;
+      }
+      clearSelection(selection);
+      onChange();
+      return;
+    }
+    if (e.key === "Enter") {
+      e.preventDefault();
+      if (hasSelection(selection)) deleteSelection(buffer, cursor, selection);
+      const line = buffer[cursor.line];
+      const rest = line.slice(cursor.col);
+      buffer[cursor.line] = line.slice(0, cursor.col);
+      buffer.splice(cursor.line + 1, 0, rest);
+      cursor.line++;
+      cursor.col = 0;
+      clearSelection(selection);
+      onChange();
+      return;
+    }
+    if (e.key.length === 1) {
+      e.preventDefault();
+      if (hasSelection(selection)) deleteSelection(buffer, cursor, selection);
+      const line = buffer[cursor.line];
+      buffer[cursor.line] = line.slice(0, cursor.col) + e.key + line.slice(cursor.col);
+      cursor.col++;
+      clearSelection(selection);
+      onChange();
+    }
+  });
+}
diff --git a/lib/mouse.js b/lib/mouse.js
new file mode 100644
index 0000000..e0d10af
--- /dev/null
+++ b/lib/mouse.js
@@ -0,0 +1,65 @@
+import { escapeChar } from "./html.js";
+
+function bufferColToDomOffset(lineText, col) {
+  let offset = 0;
+  for (let i = 0; i < col && i < lineText.length; i++)
+    offset += escapeChar(lineText[i]).length;
+  return offset;
+}
+
+function findTextNode(parent, targetOffset) {
+  let remaining = targetOffset;
+  const walker = document.createTreeWalker(parent, NodeFilter.SHOW_TEXT);
+  let node;
+  while ((node = walker.nextNode())) {
+    if (remaining <= node.textContent.length)
+      return { node, offset: remaining };
+    remaining -= node.textContent.length;
+  }
+  return { node: parent, offset: parent.childNodes.length };
+}
+
+function posToElement(line, col, buffer) {
+  const spans = document.querySelectorAll("#text > span");
+  if (line >= spans.length) return null;
+  const span = spans[line];
+  const range = document.createRange();
+  const lineText = buffer[line] || "";
+  const offset = bufferColToDomOffset(lineText, col);
+  const tn = findTextNode(span, offset);
+  range.setStart(tn.node, tn.offset);
+  range.collapse(true);
+  const rect = range.getBoundingClientRect();
+  return { x: rect.left, y: rect.top, height: rect.height };
+}
+
+export function elementToPos(x, y, buffer) {
+  const spans = document.querySelectorAll("#text > span");
+  let bestLine = 0;
+  let bestDistY = Infinity;
+
+  for (let i = 0; i < spans.length; i++) {
+    const rect = spans[i].getBoundingClientRect();
+    const midY = rect.top + rect.height / 2;
+    const distY = Math.abs(y - midY);
+    if (distY < bestDistY) {
+      bestDistY = distY;
+      bestLine = i;
+    }
+  }
+
+  let bestCol = 0;
+  let bestDistX = Infinity;
+  const lineText = buffer[bestLine] || "";
+  for (let c = 0; c <= lineText.length; c++) {
+    const pos = posToElement(bestLine, c, buffer);
+    if (!pos) continue;
+    const dist = Math.abs(x - pos.x);
+    if (dist < bestDistX) {
+      bestDistX = dist;
+      bestCol = c;
+    }
+  }
+
+  return { line: bestLine, col: bestCol };
+}
diff --git a/lib/render.js b/lib/render.js
new file mode 100644
index 0000000..11ff378
--- /dev/null
+++ b/lib/render.js
@@ -0,0 +1,40 @@
+export function render(buffer, cursor, selection) {
+  const range = selectedRange(selection);
+
+  const html = buffer.map((line, i) => {
+    const chars = [];
+    for (let c = 0; c <= line.length; c++) {
+      if (i === cursor.line && c === cursor.col)
+        chars.push(`<span class="cursor"></span>`);
+      if (c < line.length) {
+        const inSel = range &&
+          (i > range.start.line || (i === range.start.line && c >= range.start.col)) &&
+          (i < range.end.line || (i === range.end.line && c < range.end.col));
+        const ch = escapeChar(line[c]);
+        chars.push(inSel ? `<span class="selection">${ch}</span>` : ch);
+      }
+    }
+    if (i === cursor.line && cursor.col >= line.length)
+      chars.push(`<span class="cursor"></span>`);
+    return `<span>${chars.join("")}</span>`;
+  });
+
+  document.getElementById("text").innerHTML = html.join("<br>");
+}
+
+function selectedRange(selection) {
+  if (selection.anchor === null || selection.head === null) return null;
+  const a = selection.anchor;
+  const h = selection.head;
+  if (a.line === h.line && a.col === h.col) return null;
+  if (a.line < h.line || (a.line === h.line && a.col < h.col))
+    return { start: { ...a }, end: { ...h } };
+  return { start: { ...h }, end: { ...a } };
+}
+
+function escapeChar(c) {
+  if (c === "&") return "&amp;";
+  if (c === "<") return "&lt;";
+  if (c === ">") return "&gt;";
+  return c;
+}
diff --git a/lib/selection.js b/lib/selection.js
new file mode 100644
index 0000000..ee2c501
--- /dev/null
+++ b/lib/selection.js
@@ -0,0 +1,38 @@
+export function hasSelection(selection) {
+  return selection.anchor !== null &&
+    (selection.anchor.line !== selection.head.line ||
+      selection.anchor.col !== selection.head.col);
+}
+
+export function selectedRange(selection) {
+  if (selection.anchor === null || selection.head === null) return null;
+  const a = selection.anchor;
+  const h = selection.head;
+  if (a.line === h.line && a.col === h.col) return null;
+  if (a.line < h.line || (a.line === h.line && a.col < h.col))
+    return { start: { ...a }, end: { ...h } };
+  return { start: { ...h }, end: { ...a } };
+}
+
+export function clearSelection(selection) {
+  selection.anchor = null;
+  selection.head = null;
+}
+
+export function deleteSelection(buffer, cursor, selection) {
+  const range = selectedRange(selection);
+  if (!range) return;
+  const { start, end } = range;
+  if (start.line === end.line) {
+    const line = buffer[start.line];
+    buffer[start.line] = line.slice(0, start.col) + line.slice(end.col);
+  } else {
+    const before = buffer[start.line].slice(0, start.col);
+    const after = buffer[end.line].slice(end.col);
+    buffer[start.line] = before + after;
+    buffer.splice(start.line + 1, end.line - start.line);
+  }
+  cursor.line = start.line;
+  cursor.col = start.col;
+  clearSelection(selection);
+}
diff --git a/main.js b/main.js
index ef67114..633fad6 100644
--- a/main.js
+++ b/main.js
@@ -1,11 +1,12 @@
-import { render } from "./render.js";
-import { setupInput } from "./input.js";
+import { render } from "./lib/render.js";
+import { setupInput } from "./lib/keyboard.js";
 
 const buffer = ["Hello, world!", "Second line."];
 const cursor = { line: 0, col: 0 };
+const selection = { anchor: null, head: null };
 
 function onChange() {
-  render(buffer, cursor);
+  render(buffer, cursor, selection);
   try {
     console.log(buffer.map((line) => JSON.parse(App.testing(line))));
   } catch (e) {
@@ -14,7 +15,5 @@ function onChange() {
   document.getElementById("text").innerHTML += "<br>";
 }
 
-function escapeHtml(s) {}
-
-setupInput(buffer, cursor, onChange);
-render(buffer, cursor);
+setupInput(buffer, cursor, selection, onChange);
+render(buffer, cursor, selection);
diff --git a/render.js b/render.js
deleted file mode 100644
index d8bd1a2..0000000
--- a/render.js
+++ /dev/null
@@ -1,13 +0,0 @@
-export function render(buffer, cursor) {
-  const html = buffer.map((line, i) => {
-    if (i !== cursor.line) return `<span>${escapeHtml(line)}</span>`;
-    const before = escapeHtml(line.slice(0, cursor.col));
-    const after = escapeHtml(line.slice(cursor.col));
-    return `<span>${before}<span class="cursor"></span>${after}</span>`;
-  });
-  document.getElementById("text").innerHTML = html.join("<br>");
-}
-
-function escapeHtml(s) {
-  return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
-}