diff --git a/include/mrk/ast.h b/include/mrk/ast.h
index 0ca008f..1e3adc2 100644
--- a/include/mrk/ast.h
+++ b/include/mrk/ast.h
@@ -8,7 +8,9 @@
 #define MRK_AST_NODE_ARGS 1
 
 typedef enum mrk_ast_node_type {
-  mrk_ast_node_type_header = 0,
+  mrk_ast_node_type_none = 0,
+  mrk_ast_node_type_header,
+  mrk_ast_node_type_sentence,
 } mrk_ast_node_type;
 
 typedef struct mrk_ast_node {
@@ -17,7 +19,10 @@ typedef struct mrk_ast_node {
     size_t len;
   } children;
   mrk_ast_node_type type;
-  void *args[MRK_AST_NODE_ARGS];
+  struct {
+    void *ptr;
+    size_t num;
+  } args[MRK_AST_NODE_ARGS];
 } mrk_ast_node;
 
 /**
diff --git a/include/mrk/common.h b/include/mrk/common.h
index f621949..3a8094c 100644
--- a/include/mrk/common.h
+++ b/include/mrk/common.h
@@ -30,6 +30,8 @@
 typedef enum mrk_err {
   mrk_err_ok = 0,
   mrk_err_failed_alloc,
+  mrk_err_unexpected_token,
+  mrk_err_invalid,
 } mrk_err;
 
 #endif
diff --git a/include/mrk/lexer.h b/include/mrk/lexer.h
index 49c7af9..bb181c0 100644
--- a/include/mrk/lexer.h
+++ b/include/mrk/lexer.h
@@ -37,6 +37,7 @@ typedef enum mrk_token_type {
   mrk_token_type_word,
   mrk_token_type_checked_box,
   mrk_token_type_unchecked_box,
+  mrk_token_type_text,
 } mrk_token_type;
 
 typedef struct mrk_token {
@@ -45,6 +46,17 @@ typedef struct mrk_token {
   size_t end;
 } mrk_token;
 
+/**
+ * Return the length of the given token.
+ */
+size_t mrk_token_len(mrk_token t);
+
+/**
+ * Return a pointer to the start of the lexeme in the initial buffer, returning
+ * the length of the lexeme.
+ */
+size_t mrk_token_lexeme(const char **out, mrk_lexer *lexer, mrk_token t);
+
 /**
  * Initialize a new lexer struct.
  */
diff --git a/include/mrk/parser.h b/include/mrk/parser.h
index ace979c..8bd0c33 100644
--- a/include/mrk/parser.h
+++ b/include/mrk/parser.h
@@ -5,6 +5,8 @@
 #include "mrk/common.h"
 #include "mrk/lexer.h"
 
+#define MRK_MAX_HEADER_LEN 6
+
 typedef struct mrk_parser mrk_parser;
 
 /**
diff --git a/src/_include/mrk/parser_internal.h b/src/_include/mrk/parser_internal.h
index 9a567c1..86b1953 100644
--- a/src/_include/mrk/parser_internal.h
+++ b/src/_include/mrk/parser_internal.h
@@ -5,6 +5,10 @@
 #include "mrk/parser.h"
 
 #define MRK_PARSER_LOOKAHEAD_BUF_SIZE 4
+#define MRK_PARSE_ERR(p, t, m)                                                 \
+  p->error.token = t;                                                          \
+  p->error.msg = m;                                                            \
+  return mrk_err_invalid
 
 struct mrk_parser {
   mrk_lexer *lexer;
@@ -12,6 +16,10 @@ struct mrk_parser {
     mrk_token buf[MRK_PARSER_LOOKAHEAD_BUF_SIZE];
     size_t index;
   } lookahead;
+  struct {
+    mrk_token token;
+    const char *msg;
+  } error;
 };
 
 /**
@@ -34,4 +42,6 @@ void mrk_parser_advance(mrk_parser *parser);
 
 mrk_err mrk_parser_parse_block(mrk_ast_node **out, mrk_parser *parser);
 
+mrk_err mrk_parser_parse_header(mrk_ast_node **out, mrk_parser *parser);
+
 #endif
diff --git a/src/lexer/lexer.c b/src/lexer/lexer.c
index eed61ff..20efe96 100644
--- a/src/lexer/lexer.c
+++ b/src/lexer/lexer.c
@@ -129,6 +129,126 @@ void mrk_lexer_emit(mrk_token *out, mrk_lexer *lexer, mrk_token_type type) {
   lexer->token.emitted = true;
 }
 
+void mrk_lexer_lex_special(mrk_token *out, mrk_lexer *lexer) {
+  char c = mrk_lexer_advance(lexer);
+  switch (c) {
+  // All these characters have multiple meanings depending on their location
+  // in the file and how many there are, so the lexer can only match them as
+  // one or more grouped characters
+  case '#':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_pounds);
+    break;
+  case '`':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_backticks);
+    break;
+  case '-':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_dashes);
+    break;
+  case '_':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_underscores);
+    break;
+  case '*':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_stars);
+    break;
+  case '=':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_equals);
+    break;
+  case '\t':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_tabs);
+    break;
+  case '>':
+    mrk_lexer_advance_eq(lexer, c);
+    mrk_lexer_emit(out, lexer, mrk_token_type_right_angle_brackets);
+    break;
+  case '!':
+    mrk_lexer_emit(out, lexer, mrk_token_type_bang);
+    break;
+  case '[':
+    // Checkboxes for lists are lexed separately to simplify the parser later
+    // on
+    if (mrk_lexer_peek_str(lexer, " ]")) {
+      mrk_lexer_advance_n(lexer, 2);
+      mrk_lexer_emit(out, lexer, mrk_token_type_unchecked_box);
+    } else if (mrk_lexer_peek_str(lexer, "x]")) {
+      mrk_lexer_advance_n(lexer, 2);
+      mrk_lexer_emit(out, lexer, mrk_token_type_checked_box);
+    } else {
+      mrk_lexer_emit(out, lexer, mrk_token_type_left_bracket);
+    }
+    break;
+  case ']':
+    mrk_lexer_emit(out, lexer, mrk_token_type_right_bracket);
+    break;
+  case '(':
+    mrk_lexer_emit(out, lexer, mrk_token_type_left_paren);
+    break;
+  case ')':
+    mrk_lexer_emit(out, lexer, mrk_token_type_right_paren);
+    break;
+  case '\\':
+    if (mrk_lexer_peek(lexer) == '\n') {
+      mrk_lexer_emit(out, lexer, mrk_token_type_line_break);
+    } else {
+      mrk_lexer_emit(out, lexer, mrk_token_type_backslash);
+    }
+    break;
+    // Two consecutive newlines constitute a blank line, otherwise they're
+    // ignored as whitespace
+  case '\n':
+    if (mrk_lexer_peek(lexer) == '\n') {
+      mrk_lexer_advance(lexer);
+      mrk_lexer_emit(out, lexer, mrk_token_type_blank_line);
+    } else {
+      mrk_lexer_emit(out, lexer, mrk_token_type_newline);
+    }
+    break;
+  case ' ': {
+    // Either a double space or a line break
+    if (mrk_lexer_peek_str(lexer, " \n")) {
+      mrk_lexer_advance_n(lexer, 2);
+
+      mrk_lexer_emit(out, lexer, mrk_token_type_line_break);
+    } else {
+      mrk_lexer_advance_eq(lexer, ' ');
+      mrk_lexer_emit(out, lexer, mrk_token_type_spaces);
+    }
+  } break;
+  default: {
+    // Match ordered list headers
+    if (isdigit(c)) {
+      mrk_lexer_advance(lexer);
+
+      while (isdigit(mrk_lexer_peek(lexer))) {
+        mrk_lexer_advance(lexer);
+      }
+
+      if (mrk_lexer_peek(lexer) == '.') {
+        mrk_lexer_advance(lexer);
+        mrk_lexer_emit(out, lexer, mrk_token_type_dotted_number);
+      }
+      // Doesn't end with a dot, so it's just a word that happens to start
+      // with a number
+      else {
+        mrk_lexer_advance_word(lexer);
+        mrk_lexer_emit(out, lexer, mrk_token_type_word);
+      }
+    }
+    // Any other special scenarios we simply parse as a word
+    else {
+      mrk_lexer_advance_word(lexer);
+      mrk_lexer_emit(out, lexer, mrk_token_type_word);
+    }
+  } break;
+  }
+}
+
 mrk_lexer_err mrk_lexer_next(mrk_token *out, mrk_lexer *lexer) {
   if (mrk_lexer_done(lexer)) {
     return mrk_lexer_err_done;
@@ -258,3 +378,11 @@ mrk_lexer_err mrk_lexer_next(mrk_token *out, mrk_lexer *lexer) {
 
   return lexer->token.emitted ? mrk_lexer_err_ok : mrk_lexer_err_done;
 }
+
+size_t mrk_token_len(mrk_token t) { return t.end - t.start; }
+
+size_t mrk_token_lexeme(const char **out, mrk_lexer *lexer, mrk_token t) {
+  *out = lexer->buf.s + t.start;
+
+  return t.end - t.start;
+}
diff --git a/src/parser/parser.c b/src/parser/parser.c
index 671db05..9d8a369 100644
--- a/src/parser/parser.c
+++ b/src/parser/parser.c
@@ -26,4 +26,49 @@ mrk_err mrk_parser_parse(mrk_ast_node **out, mrk_parser *parser) {
   return mrk_err_ok;
 }
 
-mrk_err mrk_parser_parse_block(mrk_ast_node **out, mrk_parser *parser) {}
+mrk_err mrk_parser_parse_block(mrk_ast_node **out, mrk_parser *parser) {
+  mrk_token t = mrk_parser_peek(parser);
+
+  mrk_err (*parse_fn)(mrk_ast_node **, mrk_parser *) = NULL;
+
+  switch (t.type) {
+  case mrk_token_type_pounds: {
+    parse_fn = mrk_parser_parse_header;
+    break;
+  }
+  }
+
+  if (parse_fn == NULL) {
+    MRK_PARSE_ERR(parser, t, "Unexpected token.");
+  }
+
+  return parse_fn(out, parser);
+}
+
+/* mrk_err mrk_parser_parse_ */
+
+mrk_err mrk_parser_parse_header(mrk_ast_node **out, mrk_parser *parser) {
+  mrk_token t = mrk_parser_peek(parser);
+
+  if (mrk_token_len(t) > MRK_MAX_HEADER_LEN) {
+    MRK_PARSE_ERR(parser, t, "Headers can be at most 6 levels deep.");
+  }
+
+  mrk_parser_advance(parser);
+
+  mrk_ast_node *header;
+  MRK_RES(mrk_ast_node_init(&header));
+  header->args[0].num = mrk_token_len(t);
+
+  // Headers are blocks of their own, so they're delimited by blank lines
+  while (!mrk_parser_done(parser) &&
+         (t = mrk_parser_peek(parser)).type != mrk_token_type_blank_line) {
+    switch (t.type) { /* case */ }
+  }
+
+  // Skip blank line
+  mrk_parser_advance(parser);
+
+  *out = header;
+  return mrk_err_ok;
+}