diff --git a/as/CMakeLists.txt b/as/CMakeLists.txt
new file mode 100644
index 0000000..e2062c2
--- /dev/null
+++ b/as/CMakeLists.txt
@@ -0,0 +1,9 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(6502 VERSION 0.1.0 LANGUAGES C)
+
+subdirs(libcollect)
+include_directories(libcollect/include)
+
+add_executable(6502-as main.c as.h as.c)
+target_link_libraries(6502-as collect)
diff --git a/as/as.c b/as/as.c
new file mode 100644
index 0000000..61ad6bd
--- /dev/null
+++ b/as/as.c
@@ -0,0 +1,439 @@
+#include "as.h"
+#include "../cpu.h"
+#include "../instructions.h"
+#include "../mnemonics.h"
+
+#include <collect/map.h>
+#include <collect/vector.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdbool.h>
+
+enum
+{
+	ARG_16,						/* Absolute 16 bit argument */
+	ARG_8,						/* Absolute 8 bit argument */
+	ARG_8REL,					/* Relative 8 bit argument */
+	ARG_REL,					/* Relative label */
+	ARG_ABS,					/* Absolute label */
+	ARG_IMP,					/* Implied argument */
+};
+
+typedef struct
+{
+	uint8_t opcode;
+	uint8_t arg_type;
+	union
+	{
+		char label[32];
+		uint16_t long_arg;
+		uint8_t byte_arg;
+		int8_t rel_arg;
+	};
+} inst_t;
+
+void print_inst(inst_t *arg)
+{
+	char *arg_types =
+		"16  8   8RELREL ABS IMP ";
+	
+	printf("\033[33mInst: %.4s $%x ", arg_types + arg->arg_type * 4, arg->opcode);
+
+	switch (arg->arg_type)
+	{
+	case ARG_16:
+		printf("%x", arg->long_arg);
+		break;
+	case ARG_8:
+		printf("%x", arg->byte_arg);
+		break;
+	case ARG_8REL:
+		printf("%d", arg->rel_arg);
+		break;
+	case ARG_REL:
+	case ARG_ABS:
+		printf("%s", arg->label);
+		break;
+	}
+
+	printf("\033[0m\n");
+}
+
+bool is_ident(char c)
+{
+	return c && (isalpha(c) || isdigit(c));
+}
+
+uint32_t skip_ws(char **code)
+{
+	uint32_t len = 0;
+
+	for (; isspace(**code); (*code)++, len++)
+	{}
+
+	return len;
+}
+
+uint32_t skip_to_eol(char **code)
+{
+	uint32_t len = 0;
+
+	for (; **code && **code != '\n'; (*code)++, len++)
+	{}
+
+	if (**code)
+		(*code)++;
+
+	return len;
+}
+
+char *parse_label_name(char **code)
+{
+	char *start = *code;
+	for (; is_ident(**code); (*code)++)
+	{}
+
+	if (start == *code)
+		return false;
+
+	**code = 0;
+	return start;
+}
+
+char *parse_label(char **code)
+{
+	char *start = *code;
+
+	for (; is_ident(**code); (*code)++)
+	{}
+
+	skip_ws(code);
+
+	if (**code == ':')
+	{
+		**code = 0;
+		(*code)++;
+		return start;
+	}
+
+	*code = start;
+
+	return NULL;
+}
+
+char *parse_inst(char **code)
+{
+	char *start = *code;
+
+	for (; isalpha(**code); (*code)++)
+	{}
+
+	**code = 0;
+
+	if (start == *code)
+		return NULL;
+
+	(*code)++;
+	return start;
+}
+
+bool is_eol(char c)
+{
+	return c == ';' ||
+		c == '\n' ||
+		c == '\r' ||
+		c == '\0';
+}
+
+bool skip(char **code, const char *p)
+{
+	for (; *p && *p == **code; p++, (*code)++)
+	{}
+
+	if (!*p)
+		return true;
+	return false;
+}
+
+bool parse_num(char **code, uint64_t *num)
+{
+	char *start = *code;
+	int base = 10;
+	if (**code == '$')
+	{
+		base = 16;
+		(*code)++;
+	}
+	
+	skip_ws(code);
+
+	char *endptr = *code;
+	int64_t val = strtol(*code, &endptr, base);
+
+	if (*code == endptr)
+	{
+		*code = start;
+		return false;
+	}
+	*num = val;
+	*code = endptr;
+	return true;
+}
+
+bool parse_num_max(char **code, uint64_t *num, uint64_t max)
+{
+	uint64_t n;
+	if (parse_num(code, &n))
+	{
+		if (n > max)
+			return false;
+
+		*num = n;
+		return true;
+	}
+	else return false;
+}
+
+bool parse_u8(char **code, uint8_t *num)
+{
+	uint64_t n;
+	if (!parse_num_max(code, &n, 0xFF))
+		return false;
+
+	*num = n & 0xFF;
+	return true;
+}
+
+bool parse_u16(char **code, uint16_t *num)
+{
+	uint64_t n;
+	if (!parse_num_max(code, &n, 0xFFFF))
+		return false;
+
+	*num = n & 0xFFFF;
+	return true;
+}
+
+bool ws_end(char **code)
+{
+	skip_ws(code);
+	return is_eol(**code);
+}
+
+bool parse_arg(char *code, int am, inst_t *inst)
+{
+	skip_ws(&code);
+
+	uint16_t num;
+	uint8_t num8;
+	char *lbl;
+	
+	switch (am)
+	{
+	case AM_ACC:
+	case AM_IMP:
+		printf("Trying AM_IMP on '%.8s'\n", code);
+		skip_ws(&code);
+		if (is_eol(*code))
+		{
+			inst->arg_type = ARG_IMP;
+			return ws_end(&code);
+		}
+		break;
+
+	case AM_IMM:
+		printf("Trying AM_IMM on '%.8s'\n", code);
+		if (!skip(&code, "#"))
+			return false;
+		skip_ws(&code);
+	case AM_ZP:
+		if (parse_u8(&code, &num8))
+		{
+			inst->arg_type = ARG_8;
+			inst->byte_arg = num8;
+
+			return ws_end(&code);
+		}
+		break;
+
+	case AM_ABS:
+		if (parse_u16(&code, &num))
+		{
+			inst->arg_type = ARG_16;
+			inst->long_arg = num;
+			return true;
+		}
+		else if ((lbl = parse_label_name(&code)))
+		{
+			inst->arg_type = ARG_ABS;
+			strncpy(inst->label, lbl, 32);
+			return true;
+		}
+		break;
+
+	case AM_REL:
+		if (parse_u8(&code, &num8))
+		{
+			inst->arg_type = ARG_8REL;
+			inst->rel_arg = num;
+			return ws_end(&code);
+		}
+		else if ((lbl = parse_label_name(&code)))
+		{
+			inst->arg_type = ARG_REL;
+			strncpy(inst->label, lbl, 32);
+			return ws_end(&code);
+		}
+		break;
+
+	case AM_IND:
+		if (!skip(&code,"("))
+			return false;
+		
+		if (!parse_u16(&code, &num))
+			return false;
+
+		if (!skip(&code, ")"))
+			return false;
+
+		inst->arg_type = ARG_16;
+		inst->long_arg = num;
+		return true;
+
+	case AM_AX:
+	case AM_ZPX:
+	case AM_AY:
+	case AM_ZPY:
+		if (am == AM_AX || am == AM_AY)
+		{
+			if (!parse_u16(&code, &num))
+				return false;
+			inst->arg_type = ARG_16;
+			inst->long_arg = num;
+		}
+		else
+		{
+			if (!parse_u8(&code, &num8))
+				return false;
+			inst->arg_type = ARG_8;
+			inst->byte_arg = num8;
+		}
+		if (!skip(&code, ","))
+			return false;
+
+		skip_ws(&code);
+
+		if (tolower(*code) != (am == AM_AY || am == AM_ZPY ? 'y' : 'x'))
+			return false;
+
+		return ws_end(&code);
+
+	case AM_ZIX:
+		if (!skip(&code, "("))
+			break;
+		skip_ws(&code);
+		if (!parse_u8(&code, &num8))
+			break;
+		skip_ws(&code);
+		if (!skip(&code, ","))
+			break;
+		skip_ws(&code);
+		if (tolower(*code) != 'x')
+			return false;
+		skip_ws(&code);
+
+		if (!skip(&code, ")"))
+			break;
+
+		inst->arg_type = ARG_8;
+		inst->byte_arg = num8;
+		return ws_end(&code);
+
+	case AM_ZIY:
+		if (!skip(&code, "("))
+			break;
+		skip_ws(&code);
+		if (!parse_u8(&code, &num8))
+			break;
+		skip_ws(&code);
+		if (!skip(&code, ")"))
+			break;
+		skip_ws(&code);
+		if (!skip(&code, ","))
+			break;
+		skip_ws(&code);
+		if (tolower(*code) != 'x')
+			break;
+
+		inst->arg_type = ARG_8;
+		inst->byte_arg = num8;
+		return ws_end(&code);
+	}
+	return false;
+}
+
+uint32_t assemble(char *code, FILE *out)
+{
+	uintptr_t num_insts = 0;
+	uint32_t line_no = 1;
+	map *labels = new_map();
+	vector *insts = new_vector();
+	char *line;
+
+	printf("Assembling File\n");
+	printf("%s\n", code);
+
+	line = strtok(code, "\r\n");
+	
+	while (line)
+	{
+		skip_ws(&line);
+
+		printf("\033[36m%.9s\033[0m\n", line);
+		
+		char *label = parse_label(&line),
+			*mn = parse_inst(&line);
+		int32_t mnemonic = -1;
+
+		if (label)
+		{
+			map_set(labels, label, (void *)num_insts);
+			printf("Set label %s at %lu\n", label, num_insts);
+		}
+
+		if (mn)
+		{
+#define MN(a) if (!strcasecmp(mn, #a)) \
+				mnemonic = a;		   \
+			else
+
+			MNEMONICS;
+#undef MN
+
+			printf("Got instruction %s %d\n", mn, mnemonic);
+
+			inst_t arg;
+			// printf("Parsing '%s'\n", line);
+#define INST(_mn, am, op, len) \
+			if (mnemonic == _mn && parse_arg(line, am, &arg)) \
+			{												  \
+				arg.opcode = op;							  \
+				print_inst(&arg);							  \
+			}												  \
+			else
+
+			INSTRUCTIONS
+			{
+				printf("\033[31mCould not be parsed: %s '%s'\033[0m\n", mn, line);
+			}
+#undef INST
+		}
+
+		num_insts++;
+		line = strtok(NULL, "\r\n");
+	}
+
+	free_map(labels);
+
+	return num_insts;
+}
diff --git a/as/as.h b/as/as.h
new file mode 100644
index 0000000..4e167dd
--- /dev/null
+++ b/as/as.h
@@ -0,0 +1,9 @@
+#pragma once
+
+#include <stdio.h>
+#include <stdint.h>
+
+/*
+ * @returns NULL on failure, printing info to stderr
+ */
+uint32_t assemble(char *code, FILE *out);
diff --git a/as/libcollect b/as/libcollect
new file mode 160000
index 0000000..e9ee522
--- /dev/null
+++ b/as/libcollect
@@ -0,0 +1 @@
+Subproject commit e9ee5221d307378150d2119939025b8709da178a
diff --git a/as/main.c b/as/main.c
new file mode 100644
index 0000000..cf966f8
--- /dev/null
+++ b/as/main.c
@@ -0,0 +1,44 @@
+#include "as.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <bits/getopt_core.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+	char c;
+	FILE *in = stdin,
+		*out = stdout;
+
+	while ((c = getopt(argc, argv, "i:o:")) != -1)
+	{
+		switch (c)
+		{
+		case 'i':
+			in = fopen(optarg, "r");
+			break;
+		case 'o':
+			out = fopen(optarg, "w");
+			break;
+		case 'h':
+		case '?':
+			printf("6502 assembler\n"
+				   "Usage:\n"
+				   "    -i <input> set input file (default stdin)\n"
+				   "    -o <output> set output file (default stdout)\n");
+		}
+	}
+
+	fseek(in, 0, SEEK_END);
+	ssize_t len = ftell(in);
+	fseek(in, 0, SEEK_SET);
+
+	char *text = malloc(len + 1);
+	fread(text, len, 1, in);
+	text[len] = 0;
+
+	uint32_t built = assemble(text, out);
+
+	free(text);
+}
diff --git a/as/test/test.s b/as/test/test.s
new file mode 100644
index 0000000..edca24a
--- /dev/null
+++ b/as/test/test.s
@@ -0,0 +1,5 @@
+start:
+	lda #$32 					; Store $32 in a
+	tax							; Transfer a to x
+	stx $200					; Store x at $200
+	jmp ($FFAA)					; Jump to the address at $FFAA