diff --git a/speedcat.pdb b/speedcat.pdb
new file mode 100644
index 0000000..7bf97f6
Binary files /dev/null and b/speedcat.pdb differ
diff --git a/test_type_checker.cat b/test_type_checker.cat
new file mode 100644
index 0000000..6dfcfcf
--- /dev/null
+++ b/test_type_checker.cat
@@ -0,0 +1,9 @@
+let asdf := 123.0
+let poop :: 12 as f32 + 2.0 * asdf
+
+\fn name {}
+fn name(a b: i32) i32 { }
+\fn name() {}
+\fn name(param1 param2 param3: i32, param4: u32) u32 { }
+
+name 123 456
diff --git a/type.odin b/type.odin
new file mode 100644
index 0000000..2cb2a17
--- /dev/null
+++ b/type.odin
@@ -0,0 +1,64 @@
+package main
+
+TypeKind :: enum {
+    Integer,
+    Float,
+    String,
+}
+
+Type :: struct {
+    kind: TypeKind,
+    bit_size: u8,
+    is_signed: bool,
+}
+
+FunctionType :: struct {
+    name: [dynamic]u8,
+    return_type: ^Type,
+    parameter_types: [dynamic]^Type,
+}
+
+compare_types :: proc(a: ^Type, b: ^Type) -> (ret: bool) {
+    ret = a != nil && b != nil && a.kind == b.kind && a.bit_size == b.bit_size && a.is_signed == b.is_signed
+    return
+}
+
+compare_function_types :: proc(a: ^FunctionType, b: ^FunctionType) -> (ret: bool) {
+    ret = a != nil && b != nil && compare_types(a.return_type, b.return_type)
+    if ret {
+        for &arg, i in a.parameter_types {
+            if !compare_types(arg, b.parameter_types[i]) {
+                ret = false
+                break
+            }
+        }
+    }
+    return
+}
+
+function_type_create :: proc() -> (ret: ^FunctionType) {
+    ret = new(FunctionType)
+    return
+}
+
+type_create_integer :: proc(bit_size: u8, signed: bool) -> (ret: ^Type) {
+    ret = new(Type)
+    ret.kind = .Integer
+    ret.bit_size = bit_size
+    ret.is_signed = signed
+    return
+}
+
+type_create_float :: proc(bit_size: u8) -> (ret: ^Type) {
+    ret = new(Type)
+    ret.kind = .Float
+    ret.bit_size = bit_size
+    ret.is_signed = true
+    return
+}
+
+type_create_string :: proc() -> (ret: ^Type) {
+    ret = new(Type)
+    ret.kind = .String
+    return
+}
diff --git a/type_checker.odin b/type_checker.odin
new file mode 100644
index 0000000..2bba899
--- /dev/null
+++ b/type_checker.odin
@@ -0,0 +1,294 @@
+package main
+
+import "core:fmt"
+import "core:strconv"
+
+Scope :: struct {
+    function_definitions: map[int]^FunctionType, // A map to nodes which are the function definitions
+    variable_definitions: map[int]^Type, // A map to types
+    variable_mutability_definitions: map[int]bool, // A map to a variable's mutability
+}
+
+@(private = "file")
+infer_type :: proc(parent: ^Node, child: ^Node) {
+    if child.return_type == nil {
+        #partial switch child.kind {
+        case .Integer:   child.return_type = type_create_integer(32, true)
+        case .Float:     child.return_type = type_create_float(32)
+        case .String:    child.return_type = type_create_string()
+        case .Character: child.return_type = type_create_integer(32, false)
+        }
+    } else {
+        if parent != nil {
+            parent.return_type = child.return_type
+        }
+    }
+}
+
+@(private = "file")
+is_number :: proc(node: ^Node) -> bool {
+    return node.kind == .Integer || node.kind == .Float
+}
+
+@(private = "file")
+ast_to_type :: proc(node: ^Node) -> ^Type {
+    if node.kind == .Identifier {
+        value := node.value.([dynamic]u8)
+        if value[0] == 'u' {
+            bit_size, ok := strconv.parse_u64_of_base(string(value[1:]), 10)
+            if !ok {
+                fmt.panicf("Failed to parse integer: %s", value)
+            }
+            return type_create_integer(u8(bit_size), false)
+        } else if value[0] == 'i' {
+            bit_size, ok := strconv.parse_u64_of_base(string(value[1:]), 10)
+            if !ok {
+                fmt.panicf("Failed to parse integer: %s", value)
+            }
+            return type_create_integer(u8(bit_size), true)
+        } else if value[0] == 'f' {
+            bit_size, ok := strconv.parse_u64_of_base(string(value[1:]), 10)
+            if !ok {
+                fmt.panicf("Failed to parse integer: %s", value)
+            }
+            return type_create_float(u8(bit_size))
+        } else {
+            fmt.panicf("Unhandled identifier in ast_to_type: %s", value)
+        }
+    } else {
+        fmt.panicf("Unhandled node kind in ast_to_type: {}", node.kind)
+    }
+}
+
+scope_stack := [dynamic]Scope {}
+
+scope_enter :: proc() {
+    append(&scope_stack, Scope{})
+    scope_stack[len(scope_stack) - 1].function_definitions = make(map[int]^FunctionType)
+    scope_stack[len(scope_stack) - 1].variable_definitions = make(map[int]^Type)
+}
+
+scope_leave :: proc() {
+    if len(scope_stack) == 0 {
+        fmt.panicf("Tried to leave scope when there are no scopes")
+    }
+    delete(scope_stack[len(scope_stack) - 1].function_definitions)
+    delete(scope_stack[len(scope_stack) - 1].variable_definitions)
+    pop(&scope_stack)
+}
+
+scope_variable_lookup :: proc(name: [dynamic]u8) -> ^Type {
+    name_ := name
+    for &scope in scope_stack {
+        type, ok := scope.variable_definitions[get_character_sum_of_dyn_arr(&name_)]
+        if ok {
+            return type
+        }
+    }
+    return nil
+}
+
+scope_function_lookup :: proc(name: [dynamic]u8) -> ^FunctionType {
+    name_ := name
+    for &scope in scope_stack {
+        type, ok := scope.function_definitions[get_character_sum_of_dyn_arr(&name_)]
+        if ok {
+            return type
+        }
+    }
+    return nil
+}
+
+type_check_function_call :: proc(ast: ^Node, parent_ast: ^Node, must_be_function := true) -> ^FunctionType {
+    name : [dynamic]u8
+    if ast.kind == .FunctionCall {
+        name = ast.children[0].value.([dynamic]u8)
+    } else {
+        name = ast.value.([dynamic]u8)
+    }
+    fn := scope_function_lookup(name)
+    if fn == nil {
+        if must_be_function {
+            append(&g_message_list,
+                message_create(
+                    .Error,
+                    fmt.aprintf("Undefined function: %s", name),
+                    ast.range,
+                ),
+            )
+        }
+        return nil
+    }
+
+    return fn
+}
+
+type_check :: proc(ast: ^Node, parent_ast: ^Node) {
+    #partial switch (ast.kind) {
+    case .Integer: fallthrough
+    case .Float: fallthrough
+    case .String:
+        infer_type(parent_ast, ast)
+    case .Block:
+        scope_enter()
+        functions := find_function_definitions(ast)
+        for fn, i in functions {
+            scope_stack[len(scope_stack) - 1].function_definitions[get_character_sum_of_dyn_arr(&fn.name)] = fn
+        }
+        for child in ast.children {
+            type_check(child, ast)
+        }
+        scope_leave()
+    case .FunctionCall:
+        fn := type_check_function_call(ast, parent_ast)
+        if fn != nil {
+            if len(fn.parameter_types) != len(ast.children) - 1 {
+                append(&g_message_list,
+                    message_create(
+                        .Error,
+                        fmt.aprintf("Function call parameter count mismatch for function `%s`: {} and {}", fn.name, len(fn.parameter_types), len(ast.children) - 1),
+                        ast.range,
+                    ),
+                )
+                break
+            }
+
+            for param, i in fn.parameter_types {
+                type_check(ast.children[i + 1], ast)
+                if !compare_types(param, ast.children[i + 1].return_type) {
+                    append(&g_message_list,
+                        message_create(
+                            .Error,
+                            fmt.aprintf("Type mismatch: {} and {}", param, ast.children[i + 1].return_type),
+                            ast.range,
+                        ),
+                    )
+                }
+            }
+        }
+    case .Identifier:
+        type := scope_variable_lookup(ast.value.([dynamic]u8))
+        if type == nil {
+            fn := type_check_function_call(ast, parent_ast, false)
+            if fn == nil {
+                append(&g_message_list,
+                    message_create(
+                        .Error,
+                        fmt.aprintf("Undefined variable: %s", ast.value.([dynamic]u8)),
+                        ast.range,
+                    ),
+                )
+            } else {
+                ast.return_type = fn.return_type
+            }
+        }
+        ast.return_type = type
+    case .BinaryExpression:
+        type_check(ast.children[0], ast)
+        type_check(ast.children[1], ast)
+
+        if !compare_types(ast.children[0].return_type, ast.children[1].return_type) {
+            append(&g_message_list,
+                message_create(
+                    .Error,
+                    fmt.aprintf("Type mismatch: {} and {}", ast.children[0].return_type, ast.children[1].return_type),
+                    ast.range,
+                ),
+            )
+        }
+
+        if ast.value_token_kind == .Assign {
+            if !scope_stack[len(scope_stack) - 1].variable_mutability_definitions[get_character_sum_of_dyn_arr(&ast.children[0].value.([dynamic]u8))] {
+                append(&g_message_list,
+                    message_create(
+                        .Error,
+                        fmt.aprintf("Variable is not mutable: {}", ast.children[0].value.([dynamic]u8)),
+                        ast.range,
+                    ),
+                )
+            }
+        }
+
+        ast.return_type = ast.children[0].return_type
+
+        // FIXME: Verify that the operation is possible
+    case .UnaryExpression:
+        // FIXME: Verify that the operation is possible
+        type_check(ast.children[0], ast)
+    case .Cast:
+        type_check(ast.children[0], ast)
+        type_to := ast_to_type(ast.children[1])
+        // FIXME: Check if compatible
+        ast.return_type = type_to
+    case .BitwiseCast:
+        type_check(ast.children[0], ast)
+        // FIXME: Check if they are both the same bit size
+        ast.return_type = ast_to_type(ast.children[1])
+    case .VariableDeclaration:
+        type_check(ast.children[2], ast)
+        if ast.children[1] == nil {
+            ast.return_type = ast.children[2].return_type
+        }
+        if !compare_types(ast.return_type, ast.children[2].return_type) {
+            append(&g_message_list,
+                message_create(
+                    .Error,
+                    fmt.aprintf("Type mismatch: {} and {}", ast.return_type, ast.children[2].return_type),
+                    ast.range,
+                ),
+            )
+        }
+        scope_stack[len(scope_stack) - 1].variable_definitions[get_character_sum_of_dyn_arr(&ast.children[0].value.([dynamic]u8))] = ast.return_type
+    case .Function:
+        // FIXME: Declare variables from params
+        type_check(ast.children[1], ast)
+    case:
+        fmt.panicf("Unhandled node kind in type_check: {}", ast.kind)
+    }
+}
+
+find_function_definitions :: proc(ast_: ^Node) -> (ret: [dynamic]^FunctionType) {
+    if ast_.kind != .Block {
+        return
+    }
+    for ast in ast_.children {
+        if ast == nil {
+            continue
+        }
+        #partial switch (ast.kind) {
+        case .Function:
+            for fn in ret {
+                if compare_dyn_arrs(&fn.name, &ast.value.([dynamic]u8)) {
+                    append(&g_message_list,
+                        message_create(
+                            .Error,
+                            fmt.aprintf("Function already defined: {}", ast.value.([dynamic]u8)),
+                            ast.range,
+                        ),
+                    )
+                    continue
+                }
+            }
+            fn := function_type_create()
+            fn.name = ast.value.([dynamic]u8)
+            return_type : ^Type
+            if ast.children[0] == nil {
+                return_type = type_create_integer(0, false)
+            } else {
+                return_type = ast_to_type(ast.children[0])
+            }
+            node_print(ast)
+            for decl, i in ast.children {
+                if i < 2 {
+                    continue
+                }
+                type := ast_to_type(decl.children[1])
+                append(&fn.parameter_types, type)
+            }
+            fmt.printf("Added: %s\n", fn.name)
+            append(&ret, fn)
+        case:
+        }
+    }
+    return
+}
diff --git a/util.odin b/util.odin
index 48319ed..154b550 100644
--- a/util.odin
+++ b/util.odin
@@ -12,6 +12,18 @@ compare_dyn_arr_string :: proc(a: ^[dynamic]u8, b: string) -> bool {
 	return true
 }
 
+compare_dyn_arrs :: proc(a: ^[dynamic]u8, b: ^[dynamic]u8) -> bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for c, i in a {
+		if c != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
 get_character_sum_of_dyn_arr :: proc(a: ^[dynamic]u8) -> int {
 	sum := 0
 	for c in a {