diff --git a/src/Data/Filterable.purs b/src/Data/Filterable.purs
index a19c093..750ca82 100644
--- a/src/Data/Filterable.purs
+++ b/src/Data/Filterable.purs
@@ -15,6 +15,22 @@ module Data.Filterable
   , filterDefaultPartitionMap
   , filterMapDefault
   , cleared
+  , class FilterableWithIndex
+  , ipartitionMap
+  , ipartition
+  , ifilterMap
+  , ifilter
+  , ieitherBool
+  , ipartitionDefault
+  , ipartitionDefaultFilter
+  , ipartitionDefaultFilterMap
+  , ipartitionMapDefault
+  , imaybeBool
+  , ifilterDefault
+  , ifilterDefaultPartition
+  , ifilterDefaultPartitionMap
+  , ifilterMapDefault
+  , icleared
   , module Data.Compactable
   ) where
 
@@ -24,7 +40,9 @@ import Data.Array (partition, mapMaybe, filter) as Array
 import Data.Compactable (class Compactable, compact, separate)
 import Data.Either (Either(..))
 import Data.Foldable (foldl, foldr)
+import Data.FoldableWithIndex (foldlWithIndex)
 import Data.Functor (class Functor, map)
+import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
 import Data.HeytingAlgebra (not)
 import Data.List (List(..), filter, mapMaybe) as List
 import Data.Map (Map, empty, insert, alter, toUnfoldable) as Map
@@ -34,6 +52,88 @@ import Data.Semigroup ((<>))
 import Data.Tuple (Tuple(..))
 import Prelude (const, class Ord)
 
+class (Filterable f, FunctorWithIndex i f) <= FilterableWithIndex i f | f -> i where
+  ipartitionMap :: forall a l r.
+    (i -> a -> Either l r) -> f a -> { left :: f l, right :: f r }
+
+  ipartition :: forall a.
+    (i -> a -> Boolean) -> f a -> { no :: f a, yes :: f a }
+
+  ifilterMap :: forall a b.
+    (i -> a -> Maybe b) -> f a -> f b
+
+  ifilter :: forall a.
+    (i -> a -> Boolean) -> f a -> f a
+
+-- | Upgrade a boolean-style predicate to an either-style predicate mapping.
+ieitherBool :: forall a i. 
+  (i -> a -> Boolean) -> i -> a -> Either a a
+ieitherBool p i x = if p i x then Right x else Left x
+
+-- | Upgrade a boolean-style predicate to a maybe-style predicate mapping.
+imaybeBool :: forall a i. 
+  (i -> a -> Boolean) -> i -> a -> Maybe a
+imaybeBool p i x = if p i x then Just x else Nothing
+
+-- | A default implementation of `ipartitionMap` using `separate`. Note that this is
+-- | almost certainly going to be suboptimal compared to direct implementations.
+ipartitionMapDefault :: forall f a l r i. FilterableWithIndex i f => 
+  (i -> a -> Either l r) -> f a -> { left :: f l, right :: f r }
+ipartitionMapDefault p = separate <<< mapWithIndex p
+
+-- | A default implementation of `ipartition` using `ipartitionMap`.
+ipartitionDefault :: forall f i a. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> { no :: f a, yes :: f a }
+ipartitionDefault p xs = let o = ipartitionMap (ieitherBool p) xs in {no: o.left, yes: o.right}
+
+-- | A default implementation of `ipartition` using `ifilter`. Note that this is
+-- | almost certainly going to be suboptimal compared to direct implementations.
+ipartitionDefaultFilter :: forall f a i. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> { no :: f a, yes :: f a }
+ipartitionDefaultFilter p xs = { yes: ifilter p xs, no: ifilter (not p) xs }
+
+-- | A default implementation of `ifilterMap` using `separate`. Note that this is
+-- | almost certainly going to be suboptimal compared to direct implementations.
+ifilterMapDefault :: forall f i a b. FilterableWithIndex i f => 
+  (i -> a -> Maybe b) -> f a -> f b
+ifilterMapDefault p = compact <<< mapWithIndex p
+
+-- | A default implementation of `ipartition` using `ifilterMap`. Note that this
+-- | is almost certainly going to be suboptimal compared to direct
+-- | implementations.
+ipartitionDefaultFilterMap :: forall f i a. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> { no :: f a, yes :: f a }
+ipartitionDefaultFilterMap p xs = {yes: ifilterMap (imaybeBool p) xs, no: ifilterMap (imaybeBool (not p)) xs}
+
+-- | A default implementation of `ifilter` using `ifilterMap`.
+ifilterDefault :: forall f i a. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> f a
+ifilterDefault = ifilterMap <<< imaybeBool
+
+-- | A default implementation of `ifilter` using `ipartition`.
+ifilterDefaultPartition :: forall f i a. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> f a
+ifilterDefaultPartition p xs = (ipartition p xs).yes
+
+-- | A default implementation of `ifilter` using `ipartitionMap`.
+ifilterDefaultPartitionMap :: forall f i a. FilterableWithIndex i f => 
+  (i -> a -> Boolean) -> f a -> f a
+ifilterDefaultPartitionMap p xs = (ipartitionMap (ieitherBool p) xs).right
+
+-- | Filter out all values.
+icleared :: forall f i a b. FilterableWithIndex i f => 
+  f a -> f b
+icleared = ifilterMap \i a -> Nothing
+
+instance filterableWithIndexArray :: FilterableWithIndex Int Array where
+  ipartitionMap p = foldlWithIndex go {left: [], right: []} where
+      go i acc x = case p i x of
+        Left l -> acc { left = acc.left <> [l] }
+        Right r -> acc { right = acc.right <> [r] }
+  ipartition p = ipartitionDefault p
+  ifilterMap p = ifilterMapDefault p
+  ifilter p = ifilterDefault p
+
 -- | `Filterable` represents data structures which can be _partitioned_/_filtered_.
 -- |
 -- | - `partitionMap` - partition a data structure based on an either predicate.
diff --git a/src/Data/Witherable.purs b/src/Data/Witherable.purs
index a55772b..4379228 100644
--- a/src/Data/Witherable.purs
+++ b/src/Data/Witherable.purs
@@ -9,6 +9,16 @@ module Data.Witherable
   , withered
   , witherDefault
   , wiltDefault
+  , class WitherableWithIndex
+  , iwilt
+  , iwither
+  , ipartitionMapByWilt
+  , ifilterMapByWither
+  , itraverseByWither
+  , iwilted
+  , iwithered
+  , iwitherDefault
+  , iwiltDefault
   , module Data.Filterable
   ) where
 
@@ -26,9 +36,56 @@ import Data.Maybe (Maybe(..))
 import Data.Monoid (class Monoid, mempty)
 import Data.Newtype (unwrap)
 import Data.Traversable (class Traversable, traverse)
+import Data.TraversableWithIndex (class TraversableWithIndex, traverseWithIndex)
 import Data.Tuple (Tuple(..))
 import Prelude (class Ord)
 
+class (TraversableWithIndex i t, Witherable t) <= WitherableWithIndex i t | t -> i where
+  iwilt :: forall m a l r. Applicative m =>
+    (i -> a -> m (Either l r)) -> t a -> m { left :: t l, right :: t r }
+
+  iwither :: forall m a b. Applicative m =>
+    (i -> a -> m (Maybe b)) -> t a -> m (t b)
+
+-- | A default implementation of `iwilt` using `separate`
+iwiltDefault :: forall t m a l r i. WitherableWithIndex i t => Applicative m =>
+  (i -> a -> m (Either l r)) -> t a -> m { left :: t l, right :: t r }
+iwiltDefault p = map separate <<< traverseWithIndex p
+
+-- | A default implementation of `iwither` using `compact`.
+iwitherDefault :: forall t m a b i. WitherableWithIndex i t => Applicative m =>
+  (i -> a -> m (Maybe b)) -> t a -> m (t b)
+iwitherDefault p = map compact <<< traverseWithIndex p
+
+-- | A default implementation of `ipartitionMap` given a `WitherableWithIndex`.
+ipartitionMapByWilt :: forall t a l r i. WitherableWithIndex i t =>
+  (i -> a -> Either l r) -> t a -> { left :: t l, right :: t r }
+ipartitionMapByWilt p = unwrap <<< iwilt (\i a -> Identity (p i a))
+
+-- | A default implementation of `ifilterMap` given a `WitherableWithIndex`.
+ifilterMapByWither :: forall t a b i. WitherableWithIndex i t =>
+  (i -> a -> Maybe b) -> t a -> t b
+ifilterMapByWither p = unwrap <<< iwither (\i a -> Identity (p i a))
+
+-- | A default implementation of `itraverse` given a `WitherableWithIndex`.
+itraverseByWither :: forall t m a b i. WitherableWithIndex i t => Applicative m =>
+  (i -> a -> m b) -> t a -> m (t b)
+itraverseByWither f = iwither (\i a -> map Just (f i a))
+
+-- | Partition between `Left` and `Right` values - with effects in `m`.
+iwilted :: forall t m l r i. WitherableWithIndex i t => Applicative m =>
+  t (m (Either l r)) -> m { left :: t l, right :: t r }
+iwilted = iwilt (\i a -> a)
+
+-- | Filter out all the `Nothing` values - with effects in `m`.
+iwithered :: forall t m x i. WitherableWithIndex i t => Applicative m =>
+  t (m (Maybe x)) -> m (t x)
+iwithered = iwither (\i a -> a)
+
+instance iwitherableArray :: WitherableWithIndex Int Array where
+  iwilt = iwiltDefault
+  iwither = iwitherDefault
+
 -- | `Witherable` represents data structures which can be _partitioned_ with
 -- | effects in some `Applicative` functor.
 -- |