diff --git a/src/root.zig b/src/root.zig
index 3c7a5a7..05c764c 100644
--- a/src/root.zig
+++ b/src/root.zig
@@ -13,8 +13,5 @@ test {
     // _ = @import("theory_v1/note.zig");
     // _ = @import("theory_v1/pitch.zig");
     // _ = @import("theory_v1/scale.zig");
-    _ = @import("theory_v2/interval.zig");
-    _ = @import("theory_v2/note.zig");
-    _ = @import("theory_v2/pitch.zig");
-    _ = @import("theory_v2/scale.zig");
+    _ = @import("theory/note.zig");
 }
diff --git a/src/theory/constants.zig b/src/theory/constants.zig
new file mode 100644
index 0000000..8ddd4fd
--- /dev/null
+++ b/src/theory/constants.zig
@@ -0,0 +1,8 @@
+/// The maximum valid MIDI note number.
+pub const midi_max = 127;
+
+/// The number of notes per octave.
+pub const notes_per_oct = 7;
+
+/// The number of semitones per octave.
+pub const semis_per_oct = 12;
diff --git a/src/theory/note.zig b/src/theory/note.zig
new file mode 100644
index 0000000..9c44c50
--- /dev/null
+++ b/src/theory/note.zig
@@ -0,0 +1,143 @@
+const std = @import("std");
+const testing = std.testing;
+
+const c = @import("constants.zig");
+
+pub const Note = struct {
+    midi: u7,
+
+    pub const Letter = enum { c, d, e, f, g, a, b };
+    pub const Accidental = enum { double_flat, flat, natural, sharp, double_sharp };
+
+    pub fn init(let: Letter, acc: Accidental, oct: i8) !Note {
+        const base: i16 = baseSemitones(let);
+        const offset: i4 = switch (acc) {
+            .double_flat => -2,
+            .flat => -1,
+            .natural => 0,
+            .sharp => 1,
+            .double_sharp => 2,
+        };
+        const midi = base + offset + (oct + 1) * c.semis_per_oct;
+        if (midi < 0 or c.midi_max < midi) {
+            return error.NoteOutOfRange;
+        }
+        return .{ .midi = @intCast(midi) };
+    }
+
+    fn baseSemitones(let: Letter) u4 {
+        return switch (let) {
+            .c => 0,
+            .d => 2,
+            .e => 4,
+            .f => 5,
+            .g => 7,
+            .a => 9,
+            .b => 11,
+        };
+    }
+
+    pub fn letter(self: Note) Letter {
+        const pc = self.pitchClass();
+        return switch (pc) {
+            0, 1 => Letter.c,
+            2, 3 => Letter.d,
+            4 => Letter.e,
+            5, 6 => Letter.f,
+            7, 8 => Letter.g,
+            9, 10 => Letter.a,
+            11 => Letter.b,
+            else => unreachable,
+        };
+    }
+
+    pub fn accidental(self: Note) Accidental {
+        const pc: i8 = self.pitchClass();
+        const let = self.letter();
+        const base = baseSemitones(let);
+        const diff = @mod(pc - base + c.semis_per_oct, c.semis_per_oct);
+        return switch (diff) {
+            10 => .double_flat,
+            11 => .flat,
+            0 => .natural,
+            1 => .sharp,
+            2 => .double_sharp,
+            else => unreachable,
+        };
+    }
+
+    pub fn octave(self: Note) i8 {
+        return @divFloor(@as(i8, self.midi), c.semis_per_oct) - 1;
+    }
+
+    pub fn pitchClass(self: Note) u4 {
+        return @intCast(@mod(self.midi, c.semis_per_oct));
+    }
+
+    pub fn format(
+        self: Note,
+        comptime fmt: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) !void {
+        _ = fmt;
+        _ = options;
+        const let = self.letter();
+        const acc = self.accidental();
+        const oct = self.octave();
+        try writer.print("{c}{s}{d}", .{
+            std.ascii.toUpper(@tagName(let)[0]),
+            switch (acc) {
+                .double_flat => "𝄫",
+                .flat => "♭",
+                .natural => "",
+                .sharp => "♯",
+                .double_sharp => "𝄪",
+            },
+            oct,
+        });
+    }
+};
+
+test "Note initialization" {
+    try testing.expectError(error.NoteOutOfRange, Note.init(.c, .flat, -1));
+    try testing.expectEqual(0, (try Note.init(.c, .natural, -1)).midi);
+    try testing.expectEqual(58, (try Note.init(.c, .double_flat, 4)).midi);
+    try testing.expectEqual(59, (try Note.init(.c, .flat, 4)).midi);
+    try testing.expectEqual(60, (try Note.init(.c, .natural, 4)).midi);
+    try testing.expectEqual(61, (try Note.init(.c, .sharp, 4)).midi);
+    try testing.expectEqual(62, (try Note.init(.c, .double_sharp, 4)).midi);
+    try testing.expectEqual(69, (try Note.init(.a, .natural, 4)).midi);
+    try testing.expectEqual(127, (try Note.init(.g, .natural, 9)).midi);
+    try testing.expectError(error.NoteOutOfRange, Note.init(.g, .sharp, 9));
+}
+
+test "Note properties" {
+    const c4 = try Note.init(.c, .natural, 4);
+    try testing.expectEqual(Note.Letter.c, c4.letter());
+    try testing.expectEqual(Note.Accidental.natural, c4.accidental());
+    try testing.expectEqual(4, c4.octave());
+    try testing.expectEqual(0, c4.pitchClass());
+
+    const cs4 = try Note.init(.c, .sharp, 4);
+    try testing.expectEqual(Note.Letter.c, cs4.letter());
+    try testing.expectEqual(Note.Accidental.sharp, cs4.accidental());
+    try testing.expectEqual(4, cs4.octave());
+    try testing.expectEqual(1, cs4.pitchClass());
+
+    // There's currently no naming persistence.
+    const df4 = try Note.init(.d, .flat, 4);
+    try testing.expectEqual(Note.Letter.c, df4.letter());
+    try testing.expectEqual(Note.Accidental.sharp, df4.accidental());
+    try testing.expectEqual(4, df4.octave());
+    try testing.expectEqual(1, df4.pitchClass());
+}
+
+test "Note formatting" {
+    // There's currently no naming persistence.
+    try testing.expectFmt("A♯3", "{}", .{try Note.init(.c, .double_flat, 4)});
+    try testing.expectFmt("B3", "{}", .{try Note.init(.c, .flat, 4)});
+    try testing.expectFmt("C4", "{}", .{try Note.init(.c, .natural, 4)});
+    try testing.expectFmt("C♯4", "{}", .{try Note.init(.c, .sharp, 4)});
+    try testing.expectFmt("D4", "{}", .{try Note.init(.c, .double_sharp, 4)});
+}