diff --git a/Data/Micro.hs b/Data/Micro.hs
--- a/Data/Micro.hs
+++ b/Data/Micro.hs
@@ -77,11 +77,6 @@
 microQuotRem (Micro a) (Micro b) = (n, Micro f) where
     (n, f) = quotRem a b
 
--- for when we'd rather not depend on RealFrac
-{-# INLINE microTruncate #-}
-microTruncate :: Micro -> Int
-microTruncate a = fromIntegral . fst . microQuotRem a $ Micro 1000000
-
 instance AdditiveGroup Micro where
     {-# INLINE zeroV #-}
     zeroV = Micro 0
diff --git a/Data/Thyme/Calendar.hs b/Data/Thyme/Calendar.hs
--- a/Data/Thyme/Calendar.hs
+++ b/Data/Thyme/Calendar.hs
@@ -21,21 +21,25 @@
 import Data.Thyme.Format.Internal
 import Data.Thyme.TH
 
-{-# INLINE gregorian #-}
-gregorian :: Simple Iso Day YearMonthDay
-gregorian = ordinalDate . iso fromOrdinal toOrdinal where
+{-# INLINE yearMonthDay #-}
+yearMonthDay :: Simple Iso OrdinalDate YearMonthDay
+yearMonthDay = iso fromOrdinal toOrdinal where
 
-    {-# INLINE fromOrdinal #-}
+    {-# INLINEABLE fromOrdinal #-}
     fromOrdinal :: OrdinalDate -> YearMonthDay
     fromOrdinal (OrdinalDate y yd) = (YearMonthDay y m d) where
         MonthDay m d = view (monthDay (isLeapYear y)) yd
 
-    {-# INLINE toOrdinal #-}
+    {-# INLINEABLE toOrdinal #-}
     toOrdinal :: YearMonthDay -> OrdinalDate
     toOrdinal (YearMonthDay y m d) = OrdinalDate y $
         review (monthDay (isLeapYear y)) (MonthDay m d)
 
-{-# INLINE fromGregorianValid #-}
+{-# INLINE gregorian #-}
+gregorian :: Simple Iso Day YearMonthDay
+gregorian = ordinalDate . yearMonthDay
+
+{-# INLINEABLE fromGregorianValid #-}
 fromGregorianValid :: YearMonthDay -> Maybe Day
 fromGregorianValid (YearMonthDay y m d) = review ordinalDate . OrdinalDate y
     <$> monthDayToDayOfYearValid (isLeapYear y) (MonthDay m d)
diff --git a/Data/Thyme/Calendar/Internal.hs b/Data/Thyme/Calendar/Internal.hs
--- a/Data/Thyme/Calendar/Internal.hs
+++ b/Data/Thyme/Calendar/Internal.hs
@@ -92,17 +92,17 @@
 
 ------------------------------------------------------------------------
 
-type Week = Int
+type WeekOfYear = Int
 type DayOfWeek = Int
 data WeekDate = WeekDate
     { wdYear :: {-# UNPACK #-}!Year
-    , wdWeek :: {-# UNPACK #-}!Week
+    , wdWeek :: {-# UNPACK #-}!WeekOfYear
     , wdDay :: {-# UNPACK #-}!DayOfWeek
     } deriving (Eq, Ord, Data, Typeable, Show)
 
 instance NFData WeekDate
 
--- | Accepts 0-based 'DayOfWeek' and 'Week' when 'review'ing.
+-- | Accepts 0-based 'DayOfWeek' and 'WeekOfYear' when 'review'ing.
 {-# INLINE weekDate #-}
 weekDate :: Simple Iso Day WeekDate
 weekDate = iso toWeek fromWeek where
@@ -114,9 +114,9 @@
         -- pilfered and refactored; no idea what foo and bar mean
         OrdinalDate y0 yd = view ordinalDate day
         d = mjd + 2
-        foo :: Year -> {-Week-1-}Int64
+        foo :: Year -> {-WeekOfYear-1-}Int64
         foo y = bar $ review ordinalDate (OrdinalDate y 6)
-        bar :: Day -> {-Week-1-}Int64
+        bar :: Day -> {-WeekOfYear-1-}Int64
         bar (ModifiedJulianDay k) = div d 7 - div k 7
         w0 = bar $ ModifiedJulianDay (d - fromIntegral yd + 4)
         (y1, w1) = case w0 of
@@ -130,7 +130,7 @@
         WeekDate _ wMax _ = toWeek $ review ordinalDate (OrdinalDate y 365)
 
 {-# INLINE fromWeekMax #-}
-fromWeekMax :: Week -> WeekDate -> Day
+fromWeekMax :: WeekOfYear -> WeekDate -> Day
 fromWeekMax wMax (WeekDate y w d) = ModifiedJulianDay mjd where
     -- pilfered and refactored
     ModifiedJulianDay k = review ordinalDate (OrdinalDate y 6)
diff --git a/Data/Thyme/Calendar/MonthDay.hs b/Data/Thyme/Calendar/MonthDay.hs
--- a/Data/Thyme/Calendar/MonthDay.hs
+++ b/Data/Thyme/Calendar/MonthDay.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TemplateHaskell #-}
 
+-- | Julian or Gregorian.
 module Data.Thyme.Calendar.MonthDay
     ( Month, DayOfMonth
     , module Data.Thyme.Calendar.MonthDay
diff --git a/Data/Thyme/Calendar/OrdinalDate.hs b/Data/Thyme/Calendar/OrdinalDate.hs
--- a/Data/Thyme/Calendar/OrdinalDate.hs
+++ b/Data/Thyme/Calendar/OrdinalDate.hs
@@ -29,7 +29,7 @@
     d = mjd + 3
     k = d - fromIntegral yd
 
--- | Accepts 0−6 for 'DayOfWeek', and 0-based 'Week's.
+-- | Accepts 0−6 for 'DayOfWeek', and 0-based 'WeekOfYear's.
 {-# INLINEABLE fromSundayStartWeekValid #-}
 fromSundayStartWeekValid :: WeekDate -> Maybe Day
 fromSundayStartWeekValid wd@(WeekDate y w d) = fromWeekMax wMax wd
@@ -45,7 +45,7 @@
     d = mjd + 2
     k = d - fromIntegral yd
 
--- | Accepts 1−7 for 'DayOfWeek', and 0-based 'Week's.
+-- | Accepts 1−7 for 'DayOfWeek', and 0-based 'WeekOfYear's.
 {-# INLINEABLE fromMondayStartWeekValid #-}
 fromMondayStartWeekValid :: WeekDate -> Maybe Day
 fromMondayStartWeekValid wd@(WeekDate y w d) = fromWeekMax wMax wd
diff --git a/Data/Thyme/Calendar/WeekDate.hs b/Data/Thyme/Calendar/WeekDate.hs
--- a/Data/Thyme/Calendar/WeekDate.hs
+++ b/Data/Thyme/Calendar/WeekDate.hs
@@ -3,7 +3,7 @@
 
 -- | ISO 8601 Week Date format
 module Data.Thyme.Calendar.WeekDate
-    ( Year, Week, DayOfWeek
+    ( Year, WeekOfYear, DayOfWeek
     , WeekDate (..), weekDate
     , module Data.Thyme.Calendar.WeekDate
     ) where
@@ -17,7 +17,7 @@
 import Data.Thyme.TH
 import Text.Printf
 
--- | Rejects 0-based 'DayOfWeek' and 'Week'.
+-- | Rejects 0-based 'DayOfWeek' and 'WeekOfYear'.
 {-# INLINEABLE fromWeekDateValid #-}
 fromWeekDateValid :: WeekDate -> Maybe Day
 fromWeekDateValid wd@(WeekDate y w d) = fromWeekMax wMax wd
diff --git a/Data/Thyme/Format.hs b/Data/Thyme/Format.hs
new file mode 100644
--- /dev/null
+++ b/Data/Thyme/Format.hs
@@ -0,0 +1,197 @@
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Data.Thyme.Format
+    ( FormatTime (..)
+    , formatTime
+    ) where
+
+import Prelude
+import Control.Applicative
+import Control.Lens
+import Data.Char
+import Data.Int
+import Data.Micro
+import Data.Thyme.Calendar
+import Data.Thyme.Calendar.OrdinalDate
+import Data.Thyme.Calendar.WeekDate
+import Data.Thyme.Calendar.MonthDay
+import Data.Thyme.Clock.POSIX
+import Data.Thyme.Clock.Scale
+import Data.Thyme.Clock.UTC
+import Data.Thyme.LocalTime
+import Data.Thyme.Format.Internal
+import System.Locale
+
+class FormatTime t where
+    showsTime :: TimeLocale -> t -> (Char -> ShowS) -> (Char -> ShowS)
+
+{-# INLINEABLE formatTime #-}
+formatTime :: (FormatTime t) => TimeLocale -> String -> t -> String
+formatTime l@TimeLocale {..} spec t = go spec "" where
+    -- leave unrecognised codes as they are
+    format = showsTime l t (\ c s -> '%' : c : s)
+    go s = case s of
+        '%' : c : rest -> case c of
+            -- aggregate
+            'c' -> go (dateTimeFmt ++ rest)
+            'r' -> go (time12Fmt ++ rest)
+            'X' -> go (timeFmt ++ rest)
+            'x' -> go (dateFmt ++ rest)
+            -- modifier (whatever)
+            '-' -> go ('%' : rest)
+            '_' -> go ('%' : rest)
+            '0' -> go ('%' : rest)
+            '^' -> go ('%' : rest)
+            '#' -> go ('%' : rest)
+            -- escape (why would anyone need %t and %n?)
+            '%' -> (:) '%' . go rest
+            -- default
+            _ -> format c . go rest
+        c : rest -> (:) c . go rest
+        [] -> id
+
+instance FormatTime TimeOfDay where
+    {-# INLINEABLE showsTime #-}
+    showsTime TimeLocale {..} (TimeOfDay h m (DiffTime s)) = \ def c -> case c of
+        -- aggregate
+        'R' -> shows02 h . (:) ':' . shows02 m
+        'T' -> shows02 h . (:) ':' . shows02 m . (:) ':' . shows02 si
+        -- AM/PM
+        'P' -> (++) $ toLower <$> if h < 12 then fst amPm else snd amPm
+        'p' -> (++) $ if h < 12 then fst amPm else snd amPm
+        -- Hour
+        'H' -> shows02 h
+        'I' -> shows02 $ 1 + mod (h - 1) 12
+        'k' -> shows_2 h
+        'l' -> shows_2 $ 1 + mod (h - 1) 12
+        -- Minute
+        'M' -> shows02 m
+        -- Second
+        'S' -> shows02 si
+        'q' -> fills06 su . shows su
+        'Q' -> if su == 0 then id else (:) '.' . fills06 su . drop0 su
+        -- default
+        _ -> def c
+
+        where
+        (fromIntegral -> si, Micro su) = microQuotRem s (Micro 1000000)
+
+        {-# INLINE fills06 #-}
+        fills06 :: Int64 -> ShowS
+        fills06 n = case () of
+            _ | n < 10 -> (:) '0' . (:) '0' . (:) '0' . (:) '0' . (:) '0'
+            _ | n < 100 -> (:) '0' . (:) '0' . (:) '0' . (:) '0'
+            _ | n < 1000 -> (:) '0' . (:) '0' . (:) '0'
+            _ | n < 10000 -> (:) '0' . (:) '0'
+            _ | n < 100000 -> (:) '0'
+            _ -> id
+
+        {-# INLINE drop0 #-}
+        drop0 :: Int64 -> ShowS
+        drop0 n = case divMod n 10 of
+            (q, 0) -> drop0 q
+            _ -> shows n
+
+instance FormatTime YearMonthDay where
+    {-# INLINEABLE showsTime #-}
+    showsTime TimeLocale {..} (YearMonthDay y m d) = \ def c -> case c of
+        -- aggregate
+        'D' -> shows02 m . (:) '/' . shows02 d . (:) '/' . shows02 (mod y 100)
+        'F' -> shows04 y . (:) '-' . shows02 m . (:) '-' . shows02 d
+        -- Year
+        'Y' -> shows04 y
+        'y' -> shows02 (mod y 100)
+        'C' -> shows02 (div y 100)
+        -- Month
+        'B' -> (++) . fst $ months !! (m - 1)
+        'b' -> (++) . snd $ months !! (m - 1)
+        'h' -> (++) . snd $ months !! (m - 1)
+        'm' -> shows02 m
+        -- DayOfMonth
+        'd' -> shows02 d
+        'e' -> shows_2 d
+        -- default
+        _ -> def c
+
+instance FormatTime MonthDay where
+    {-# INLINEABLE showsTime #-}
+    showsTime TimeLocale {..} (MonthDay m d) = \ def c -> case c of
+        -- Month
+        'B' -> (++) . fst $ months !! (m - 1)
+        'b' -> (++) . snd $ months !! (m - 1)
+        'h' -> (++) . snd $ months !! (m - 1)
+        'm' -> shows02 m
+        -- DayOfMonth
+        'd' -> shows02 d
+        'e' -> shows_2 d
+        -- default
+        _ -> def c
+
+instance FormatTime OrdinalDate where
+    {-# INLINEABLE showsTime #-}
+    showsTime TimeLocale {..} (OrdinalDate y d) = \ def c -> case c of
+        -- Year
+        'Y' -> shows04 y
+        'y' -> shows02 (mod y 100)
+        'C' -> shows02 (div y 100)
+        -- DayOfYear
+        'j' -> shows03 d
+        -- default
+        _ -> def c
+
+instance FormatTime WeekDate where
+    {-# INLINEABLE showsTime #-}
+    showsTime TimeLocale {..} (WeekDate y w d) = \ def c -> case c of
+        -- Year
+        'G' -> shows04 y
+        'g' -> shows02 (mod y 100)
+        'f' -> shows02 (div y 100)
+        -- WeekOfYear
+        'V' -> shows02 w
+        -- DayOfWeek
+        'u' -> shows d
+        'A' -> (++) . fst $ wDays !! mod d 7
+        'a' -> (++) . snd $ wDays !! mod d 7
+        'w' -> shows (mod d 7)
+        -- default
+        _ -> def c
+
+instance FormatTime LocalTime where
+    {-# INLINEABLE showsTime #-}
+    showsTime l (LocalTime day tod) = showsTime l day . showsTime l tod
+
+instance FormatTime Day where
+    {-# INLINEABLE showsTime #-}
+    showsTime l d = showsTime l ordinal
+            . showsTime l (view yearMonthDay ordinal)
+            . showsTime l (view weekDate d) . other where
+        ordinal = view ordinalDate d
+        other :: (Char -> ShowS) -> (Char -> ShowS)
+        other def c = case c of
+            -- Non-standard WeekOfYear
+            'U' -> shows02 . wdWeek $ sundayStartWeek d
+            'W' -> shows02 . wdWeek $ mondayStartWeek d
+            -- default
+            _ -> def c
+
+instance FormatTime TimeZone where
+    {-# INLINEABLE showsTime #-}
+    showsTime _ tz@(TimeZone _ _ name) = \ def c -> case c of
+        'z' -> (++) (timeZoneOffsetString tz)
+        'Z' -> (++) (if null name then timeZoneOffsetString tz else name)
+        _ -> def c
+
+instance FormatTime ZonedTime where
+    {-# INLINEABLE showsTime #-}
+    showsTime l (ZonedTime lt tz) = showsTime l lt . showsTime l tz
+
+instance FormatTime UTCTime where
+    {-# INLINEABLE showsTime #-}
+    showsTime l t = \ def c -> case c of
+        's' -> shows . fst $ microQuotRem s (Micro 1000000)
+        _ -> showsTime l (view zonedTime (utc, t)) def c
+      where
+        NominalDiffTime s = view posixTime t
+
diff --git a/Data/Thyme/Format/Internal.hs b/Data/Thyme/Format/Internal.hs
--- a/Data/Thyme/Format/Internal.hs
+++ b/Data/Thyme/Format/Internal.hs
@@ -1,26 +1,21 @@
 module Data.Thyme.Format.Internal where
 
 import Prelude
-import Data.Micro
 
 {-# INLINE shows02 #-}
 shows02 :: Int -> String -> String
 shows02 n = if n < 10 then (:) '0' . shows n else shows n
 
-{-# INLINE show02 #-}
-show02 :: Int -> String
-show02 n = if n < 10 then '0' : show n else show n
-
-{-# INLINE show_2 #-}
-show_2 :: Int -> String
-show_2 n = if n < 10 then ' ' : show n else show n
+{-# INLINE shows_2 #-}
+shows_2 :: Int -> String -> String
+shows_2 n = if n < 10 then (:) ' ' . shows n else shows n
 
-{-# INLINE show03 #-}
-show03 :: Int -> String
-show03 n = case () of
-    _ | n < 10 -> '0' : '0' : show n
-    _ | n < 100 -> '0' : show n
-    _ -> show n
+{-# INLINE shows03 #-}
+shows03 :: Int -> ShowS
+shows03 n = case () of
+    _ | n < 10 -> (:) '0' . (:) '0' . shows n
+    _ | n < 100 -> (:) '0' . shows n
+    _ -> shows n
 
 {-# INLINE shows04 #-}
 shows04 :: Int -> String -> String
@@ -29,33 +24,4 @@
     _ | n < 100 -> (:) '0' . (:) '0' . shows n
     _ | n < 1000 -> (:) '0' . shows n
     _ -> shows n
-
-{-# INLINE show04 #-}
-show04 :: Int -> String
-show04 n = shows04 n ""
-
-{-# INLINE show60 #-}
-show60 :: Micro -> String
-show60 (Micro u) = case () of
-    _ | u < 10 -> '0' : '0' : '0' : '0' : '0' : show u
-    _ | u < 100 -> '0' : '0' : '0' : '0' : show u
-    _ | u < 1000 -> '0' : '0' : '0' : show u
-    _ | u < 10000 -> '0' : '0' : show u
-    _ | u < 100000 -> '0' : show u
-    _ -> show u
-
-{-# INLINE show6 #-}
-show6 :: Micro -> String
-show6 (Micro u) = case () of
-    _ | u == 0 -> ""
-    _ | u < 10 -> '.' : '0' : '0' : '0' : '0' : '0' : shrink u
-    _ | u < 100 -> '.' : '0' : '0' : '0' : '0' : shrink u
-    _ | u < 1000 -> '.' : '0' : '0' : '0' : shrink u
-    _ | u < 10000 -> '.' : '0' : '0' : shrink u
-    _ | u < 100000 -> '.' : '0' : shrink u
-    _ -> '.' : shrink u
-  where
-    shrink v = case divMod v 10 of
-        (w, 0) -> shrink w
-        _ -> show v
 
diff --git a/thyme.cabal b/thyme.cabal
--- a/thyme.cabal
+++ b/thyme.cabal
@@ -1,5 +1,5 @@
 name:           thyme
-version:        0.1.1.0
+version:        0.1.1.1
 synopsis:       A faster time library
 description:
     A faster time library
@@ -35,6 +35,7 @@
         Data.Thyme.Calendar.WeekDate
         Data.Thyme.Clock
         Data.Thyme.Clock.POSIX
+        Data.Thyme.Format
         Data.Thyme.LocalTime
     other-modules:
         Data.Micro