diff --git a/lib/lexer_inline.js b/lib/lexer_inline.js
index 1dc68cb..6345e7b 100644
--- a/lib/lexer_inline.js
+++ b/lib/lexer_inline.js
@@ -18,6 +18,7 @@ rules.push(require('./lexer_inline/escape'));
 rules.push(require('./lexer_inline/backticks'));
 //
 //
+rules.push(require('./lexer_inline/emphasis'));
 rules.push(require('./lexer_inline/autolink'));
 rules.push(require('./lexer_inline/htmltag'));
 rules.push(require('./lexer_inline/entity'));
@@ -119,7 +120,7 @@ LexerInline.prototype.tokenize = function (state) {
   var ok, i,
       rules = this.rules,
       len = this.rules.length,
-      end = state.src.length;
+      end = state.posMax;
 
   while (state.pos < end) {
 
diff --git a/lib/lexer_inline/emphasis.js b/lib/lexer_inline/emphasis.js
new file mode 100644
index 0000000..1d6d134
--- /dev/null
+++ b/lib/lexer_inline/emphasis.js
@@ -0,0 +1,204 @@
+// Process *this* and _that_
+
+'use strict';
+
+
+function isAlphaNum(code) {
+  return (code >= 0x30 /* 0 */ && code <= 0x39 /* 9 */) ||
+         (code >= 0x41 /* A */ && code <= 0x5A /* Z */) ||
+         (code >= 0x61 /* a */ && code <= 0x7A /* z */);
+}
+
+// returns the amount of markers (1, 2, 3), or -1 on failure;
+// "start" should point at a valid marker
+function parseStart(state, start) {
+  var pos = start, lastChar, count,
+      max = Math.min(state.posMax, pos + 4),
+      marker = state.src.charCodeAt(start);
+
+  lastChar = state.pending.length !== 0 ? state.pending.charCodeAt(state.pending.length - 1) : -1;
+
+  if (lastChar === marker) { return -1; }
+
+  while (pos < max && state.src.charCodeAt(pos) === marker) { pos++; }
+  if (pos >= max) { return -1; }
+  count = pos - start;
+
+  // Quoting spec:
+  //
+  // Character can open emphasis iff
+  //  1. it is not part of a sequence of four or more unescaped markers,
+  //  2. it is not followed by whitespace,
+  //  3. it is "_" and it is not preceded by an ASCII alphanumeric character, and
+  //  4. either it is not followed by a marker or it is followed immediately by strong emphasis.
+
+  if (count >= 4) {
+    // check condition 1
+    // sequence of four or more unescaped markers can't start an emphasis
+    return -1;
+  }
+
+  // check condition 2, marker followed by whitespace
+  if (state.src.charCodeAt(pos) === 0x20) { return -1; }
+
+  if (marker === 0x5F /* _ */) {
+    // check condition 3, if it's the beginning of the word
+    // we need to look back for this
+    if (isAlphaNum(lastChar)) { return -1; }
+  }
+
+  return count;
+}
+
+// returns the amount of markers (1, 2, 3), or -1 on failure;
+// "start" should point at a valid marker
+function parseEnd(state, start) {
+  var pos = start, lastChar, count,
+      max = Math.min(state.posMax, pos + 4),
+      marker = state.src.charCodeAt(start);
+
+  lastChar = state.pending.length !== 0 ? state.pending.charCodeAt(state.pending.length - 1) : -1;
+
+  if (lastChar === marker) { return -1; }
+
+  while (pos < max && state.src.charCodeAt(pos) === marker) { pos++; }
+  count = pos - start;
+
+  // Quoting spec:
+  //
+  // Character can close emphasis iff
+  //  1. it is not part of a sequence of four or more unescaped markers,
+  //  2. it is not preceded by whitespace,
+  //  3. it is not "_" or it is not followed by an ASCII alphanumeric character
+
+  if (count >= 4) {
+    // check condition 1
+    // sequence of four or more unescaped markers can't start an emphasis
+    return -1;
+  }
+
+  // check condition 2, marker preceded by whitespace
+  if (lastChar === 0x20) { return -1; }
+
+  if (marker === 0x5F) {
+    // check condition 3, if it's the end of the word
+    if (pos < max && isAlphaNum(state.src.charCodeAt(pos))) { return -1; }
+  }
+
+  return count;
+}
+
+module.exports = function emphasis(state/*, silent*/) {
+  var startCount,
+      count,
+      oldLength,
+      oldPending,
+      found,
+      ok,
+      i,
+      oldCount,
+      newCount,
+      len,
+      rules,
+      stack,
+      breakOutOfOuterLoop,
+      max = state.posMax,
+      start = state.pos,
+      marker = state.src.charCodeAt(start);
+
+  if (marker !== 0x5F/* _ */ && marker !== 0x2A /* * */) { return false; }
+
+  startCount = parseStart(state, start);
+  if (startCount < 0) { return false; }
+
+  oldLength = state.tokens.length;
+  oldPending = state.pending;
+
+  state.pos = start + startCount;
+  stack = [ startCount ];
+  rules = state.lexer.rules;
+  len = rules.length;
+
+  while (state.pos < max) {
+    if (state.src.charCodeAt(state.pos) === marker) {
+      count = parseEnd(state, state.pos);
+      if (count >= 1) {
+        oldCount = stack.pop();
+        newCount = count;
+
+        while (oldCount !== newCount) {
+          if (oldCount === 3) {
+            // e.g. `***foo*`
+            stack.push(3 - newCount);
+            break;
+          }
+
+          if (newCount < oldCount) {
+            // assert(oldCount == 2 && newCount == 1)
+            // i.e. `**foo* bar*`
+            // not valid for now, but might be in the future
+
+            // eslint is misconfigured, so it doesn't accept "break MAIN;"
+            // here is a crappy workaround
+            breakOutOfOuterLoop = true;
+            break;
+          }
+
+          // assert(newCount > oldCount)
+          newCount -= oldCount;
+
+          if (stack.length === 0) { break; }
+          state.pos += oldCount;
+          oldCount = stack.pop();
+        }
+
+        if (breakOutOfOuterLoop) { break; }
+
+        if (stack.length === 0) {
+          startCount = oldCount;
+          found = true;
+          break;
+        }
+        state.pos += count;
+        continue;
+      }
+
+      count = parseStart(state, state.pos);
+      if (count >= 1) {
+        stack.push(count);
+        state.pos += count;
+        continue;
+      }
+    }
+
+    for (i = 0; i < len; i++) {
+      if (rules[i] !== emphasis) { ok = rules[i](state); }
+      if (ok) { break; }
+    }
+
+    if (!ok) { state.pending += state.src[state.pos++]; }
+  }
+
+  // restore old state
+  state.tokens.length = oldLength;
+  state.pending = oldPending;
+
+  if (!found) {
+    // parser failed to find ending tag, so it's not valid emphasis
+    state.pos = start;
+    return false;
+  }
+
+  // found!
+  state.posMax = state.pos;
+  state.pos = start + startCount;
+  if (state.pending) { state.pushPending(); }
+  if (startCount === 2 || startCount === 3) { state.push({ type: 'strong_open' }); }
+  if (startCount === 1 || startCount === 3) { state.push({ type: 'em_open' }); }
+  state.lexer.tokenize(state);
+  if (startCount === 1 || startCount === 3) { state.push({ type: 'em_close' }); }
+  if (startCount === 2 || startCount === 3) { state.push({ type: 'strong_close' }); }
+  state.pos = state.posMax + startCount;
+  state.posMax = max;
+  return true;
+};
diff --git a/lib/renderer.js b/lib/renderer.js
index 3fe83b6..cf6c85b 100644
--- a/lib/renderer.js
+++ b/lib/renderer.js
@@ -139,6 +139,20 @@ rules.td_close = function (/*tokens, idx, options*/) {
 };
 
 
+rules.strong_open = function(/*tokens, idx, options*/) {
+  return '<strong>';
+};
+rules.strong_close = function(/*tokens, idx, options*/) {
+  return '</strong>';
+};
+rules.em_open = function(/*tokens, idx, options*/) {
+  return '<em>';
+};
+rules.em_close = function(/*tokens, idx, options*/) {
+  return '</em>';
+};
+
+
 rules.hardbreak = function (tokens, idx, options) {
   return (options.xhtml ? '<br />' : '<br>') + '\n';
 };