diff --git a/README.md b/README.md
index dfd8034..561a81e 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,8 @@ Viper uses the following precedence order. Each item takes precedence over the i
 **Important:** Viper configuration keys are case insensitive.
 There are ongoing discussions about making that optional.
 
+Viper configuration keys are case insensitive by default. They can be made case
+sensitive with `viper.SetKeysCaseSensitive(true)`.
 
 ## Putting Values into Viper
 
diff --git a/go.mod b/go.mod
index 7d108dc..fdd0374 100644
--- a/go.mod
+++ b/go.mod
@@ -1,4 +1,4 @@
-module github.com/spf13/viper
+module github.com/gbunt/viper
 
 go 1.12
 
@@ -27,6 +27,7 @@ require (
 	github.com/spf13/cast v1.3.0
 	github.com/spf13/jwalterweatherman v1.0.0
 	github.com/spf13/pflag v1.0.3
+	github.com/spf13/viper v1.7.1
 	github.com/stretchr/testify v1.3.0
 	github.com/subosito/gotenv v1.2.0
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 // indirect
diff --git a/go.sum b/go.sum
index 463aa7d..f0297c4 100644
--- a/go.sum
+++ b/go.sum
@@ -223,6 +223,8 @@ github.com/spf13/jwalterweatherman v1.0.0 h1:XHEdyB+EcvlqZamSM4ZOMGlc93t6AcsBEu9
 github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
 github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
+github.com/spf13/viper v1.7.1 h1:pM5oEahlgWv/WnHXpgbKz7iLIxRf65tye2Ci+XFK5sk=
+github.com/spf13/viper v1.7.1/go.mod h1:8WkrPz2fc9jxqZNCJI/76HCieCp4Q8HaLFoCha5qpdg=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
diff --git a/viper.go b/viper.go
index c3130c2..64c3b05 100644
--- a/viper.go
+++ b/viper.go
@@ -199,6 +199,7 @@ type Viper struct {
 	automaticEnvApplied bool
 	envKeyReplacer      StringReplacer
 	allowEmptyEnv       bool
+	caseSensitiveKeys   bool
 
 	config         map[string]interface{}
 	override       map[string]interface{}
@@ -553,7 +554,6 @@ func (v *Viper) providerPathExists(p *defaultRemoteProvider) bool {
 
 // searchMap recursively searches for a value for path in source map.
 // Returns nil if not found.
-// Note: This assumes that the path entries and map keys are lower cased.
 func (v *Viper) searchMap(source map[string]interface{}, path []string) interface{} {
 	if len(path) == 0 {
 		return source
@@ -600,7 +600,7 @@ func (v *Viper) searchMapWithPathPrefixes(source map[string]interface{}, path []
 
 	// search for path prefixes, starting from the longest one
 	for i := len(path); i > 0; i-- {
-		prefixKey := strings.ToLower(strings.Join(path[0:i], v.keyDelim))
+		prefixKey := v.caseKey(strings.Join(path[0:i], v.keyDelim))
 
 		next, ok := source[prefixKey]
 		if ok {
@@ -722,7 +722,7 @@ func GetViper() *Viper {
 }
 
 // Get can retrieve any value given the key to use.
-// Get is case-insensitive for a key.
+// Get's case-sensitivity for key is determined by viper.keyCaseSensitivity.
 // Get has the behavior of returning the value associated with the first
 // place from where it is set. Viper will check in the following order:
 // override, flag, env, config file, key/value store, default
@@ -731,8 +731,8 @@ func GetViper() *Viper {
 func Get(key string) interface{} { return v.Get(key) }
 
 func (v *Viper) Get(key string) interface{} {
-	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey, true)
+	casedKey := v.caseKey(key)
+	val := v.find(casedKey, true)
 	if val == nil {
 		return nil
 	}
@@ -740,7 +740,7 @@ func (v *Viper) Get(key string) interface{} {
 	if v.typeByDefValue {
 		// TODO(bep) this branch isn't covered by a single test.
 		valType := val
-		path := strings.Split(lcaseKey, v.keyDelim)
+		path := strings.Split(casedKey, v.keyDelim)
 		defVal := v.searchMap(v.defaults, path)
 		if defVal != nil {
 			valType = defVal
@@ -778,7 +778,7 @@ func (v *Viper) Get(key string) interface{} {
 }
 
 // Sub returns new Viper instance representing a sub tree of this instance.
-// Sub is case-insensitive for a key.
+// Sub's case-sensitivity for key is determined by viper.keyCaseSensitivity.
 func Sub(key string) *Viper { return v.Sub(key) }
 
 func (v *Viper) Sub(key string) *Viper {
@@ -1015,7 +1015,7 @@ func (v *Viper) BindFlagValue(key string, flag FlagValue) error {
 	if flag == nil {
 		return fmt.Errorf("flag for %q is nil", key)
 	}
-	v.pflags[strings.ToLower(key)] = flag
+	v.pflags[v.caseKey(key)] = flag
 	return nil
 }
 
@@ -1031,7 +1031,7 @@ func (v *Viper) BindEnv(input ...string) error {
 		return fmt.Errorf("missing key to bind to")
 	}
 
-	key = strings.ToLower(input[0])
+	key = v.caseKey(input[0])
 
 	if len(input) == 1 {
 		envkey = v.mergeWithEnvPrefix(key)
@@ -1221,12 +1221,13 @@ func stringToStringConv(val string) interface{} {
 }
 
 // IsSet checks to see if the key has been set in any of the data locations.
-// IsSet is case-insensitive for a key.
+// IsSet is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 func IsSet(key string) bool { return v.IsSet(key) }
 
 func (v *Viper) IsSet(key string) bool {
-	lcaseKey := strings.ToLower(key)
-	val := v.find(lcaseKey, false)
+	casedKey := v.caseKey(key)
+	val := v.find(casedKey, false)
 	return val != nil
 }
 
@@ -1252,11 +1253,11 @@ func (v *Viper) SetEnvKeyReplacer(r *strings.Replacer) {
 func RegisterAlias(alias string, key string) { v.RegisterAlias(alias, key) }
 
 func (v *Viper) RegisterAlias(alias string, key string) {
-	v.registerAlias(alias, strings.ToLower(key))
+	v.registerAlias(alias, v.caseKey(key))
 }
 
 func (v *Viper) registerAlias(alias string, key string) {
-	alias = strings.ToLower(alias)
+	alias = v.caseKey(alias)
 	if alias != key && alias != v.realKey(key) {
 		_, exists := v.aliases[alias]
 
@@ -1308,17 +1309,20 @@ func (v *Viper) InConfig(key string) bool {
 }
 
 // SetDefault sets the default value for this key.
-// SetDefault is case-insensitive for a key.
+// SetDefault is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 // Default only used when no value is provided by the user via flag, config or ENV.
 func SetDefault(key string, value interface{}) { v.SetDefault(key, value) }
 
 func (v *Viper) SetDefault(key string, value interface{}) {
 	// If alias passed in, then set the proper default
-	key = v.realKey(strings.ToLower(key))
-	value = toCaseInsensitiveValue(value)
+	key = v.realKey(v.caseKey(key))
+	if !v.caseSensitiveKeys {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.caseKey(path[len(path)-1])
 	deepestMap := deepSearch(v.defaults, path[0:len(path)-1])
 
 	// set innermost value
@@ -1326,18 +1330,21 @@ func (v *Viper) SetDefault(key string, value interface{}) {
 }
 
 // Set sets the value for the key in the override register.
-// Set is case-insensitive for a key.
+// Set is case-insensitive for a key. This behavior can be modified
+// with viper.SetKeysCaseSensitive.
 // Will be used instead of values obtained via
 // flags, config file, ENV, default, or key/value store.
 func Set(key string, value interface{}) { v.Set(key, value) }
 
 func (v *Viper) Set(key string, value interface{}) {
 	// If alias passed in, then set the proper override
-	key = v.realKey(strings.ToLower(key))
-	value = toCaseInsensitiveValue(value)
+	key = v.realKey(v.caseKey(key))
+	if !v.caseSensitiveKeys {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.caseKey(path[len(path)-1])
 	deepestMap := deepSearch(v.override, path[0:len(path)-1])
 
 	// set innermost value
@@ -1426,7 +1433,9 @@ func (v *Viper) MergeConfigMap(cfg map[string]interface{}) error {
 	if v.config == nil {
 		v.config = make(map[string]interface{})
 	}
-	insensitiviseMap(cfg)
+	if !v.caseSensitiveKeys {
+		insensitiviseMap(cfg)
+	}
 	mergeMaps(cfg, v.config, nil)
 	return nil
 }
@@ -1566,7 +1575,7 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 			value, _ := v.properties.Get(key)
 			// recursively build nested maps
 			path := strings.Split(key, ".")
-			lastKey := strings.ToLower(path[len(path)-1])
+			lastKey := v.caseKey(path[len(path)-1])
 			deepestMap := deepSearch(c, path[0:len(path)-1])
 			// set innermost value
 			deepestMap[lastKey] = value
@@ -1590,7 +1599,9 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 		}
 	}
 
-	insensitiviseMap(c)
+	if !v.caseSensitiveKeys {
+		insensitiviseMap(c)
+	}
 	return nil
 }
 
@@ -1689,10 +1700,9 @@ func (v *Viper) marshalWriter(f afero.File, configType string) error {
 }
 
 func keyExists(k string, m map[string]interface{}) string {
-	lk := strings.ToLower(k)
+	ck := v.caseKey(k)
 	for mk := range m {
-		lmk := strings.ToLower(mk)
-		if lmk == lk {
+		if mk == ck {
 			return mk
 		}
 	}
@@ -1921,7 +1931,7 @@ func (v *Viper) flattenAndMergeMap(shadow map[string]bool, m map[string]interfac
 			m2 = cast.ToStringMap(val)
 		default:
 			// immediate value
-			shadow[strings.ToLower(fullKey)] = true
+			shadow[v.caseKey(fullKey)] = true
 			continue
 		}
 		// recursively merge to shadow map
@@ -1947,7 +1957,7 @@ outer:
 			}
 		}
 		// add key
-		shadow[strings.ToLower(k)] = true
+		shadow[v.caseKey(k)] = true
 	}
 	return shadow
 }
@@ -1966,7 +1976,7 @@ func (v *Viper) AllSettings() map[string]interface{} {
 			continue
 		}
 		path := strings.Split(k, v.keyDelim)
-		lastKey := strings.ToLower(path[len(path)-1])
+		lastKey := v.caseKey(path[len(path)-1])
 		deepestMap := deepSearch(m, path[0:len(path)-1])
 		// set innermost value
 		deepestMap[lastKey] = value
@@ -2009,6 +2019,22 @@ func (v *Viper) SetConfigPermissions(perm os.FileMode) {
 	v.configPermissions = perm.Perm()
 }
 
+// SetKeysCaseSensitive disables the default behaviour of
+// case-insensitivising (lowercasing) keys and preserves the key casing
+// as they are found in the config files. It is important
+// to note that operations such as set and merge when
+// case sensitivity is 'on', and whtn it is turneed 'off',
+// are incompatible. A key that is set when case sentivity
+// is 'on' may not be retrievable when case sensitivity is turned 'off',
+// as the original casing is permanently lost in the former mode.
+// That is ideally, this should only be invoked only once,
+// during initialisation, and the subsequent usage must adhere
+// to the same case sentivity.
+func SetKeysCaseSensitive(on bool) { v.SetKeysCaseSensitive(on) }
+func (v *Viper) SetKeysCaseSensitive(on bool) {
+	v.caseSensitiveKeys = on
+}
+
 func (v *Viper) getConfigType() string {
 	if v.configType != "" {
 		return v.configType
@@ -2058,6 +2084,15 @@ func (v *Viper) searchInPath(in string) (filename string) {
 	return ""
 }
 
+// caseKey cases (preserves sensitivity or lowercases) a
+// given key based on the keyCaseSensitivity config.
+func (v *Viper) caseKey(in string) (filename string) {
+	if v.caseSensitiveKeys {
+		return in
+	}
+	return strings.ToLower(in)
+}
+
 // Search all configPaths for any config file.
 // Returns the first path that exists (and is a config file).
 func (v *Viper) findConfigFile() (string, error) {
diff --git a/viper_test.go b/viper_test.go
index 09d5021..2a52838 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -1967,6 +1967,51 @@ R = 6
 	}
 }
 
+func TestCaseSensitive(t *testing.T) {
+	for _, config := range []struct {
+		typ     string
+		content string
+	}{
+		{"yaml", `
+aBcD: 1
+eF:
+  gH: 2
+  iJk: 3
+  Lm:
+    nO: 4
+    P:
+      Q: 5
+      R: 6
+`},
+		{"json", `{
+  "aBcD": 1,
+  "eF": {
+    "iJk": 3,
+    "Lm": {
+      "P": {
+        "Q": 5,
+        "R": 6
+      },
+      "nO": 4
+    },
+    "gH": 2
+  }
+}`},
+		{"toml", `aBcD = 1
+[eF]
+gH = 2
+iJk = 3
+[eF.Lm]
+nO = 4
+[eF.Lm.P]
+Q = 5
+R = 6
+`},
+	} {
+		doTestCaseSensitive(t, config.typ, config.content)
+	}
+}
+
 func TestCaseInsensitiveSet(t *testing.T) {
 	Reset()
 	m1 := map[string]interface{}{
@@ -2070,6 +2115,33 @@ func doTestCaseInsensitive(t *testing.T, typ, config string) {
 	assert.Equal(t, 5, cast.ToInt(Get("ef.lm.p.q")))
 }
 
+func doTestCaseSensitive(t *testing.T, typ, config string) {
+	Reset()
+	SetConfigType(typ)
+
+	// Turn on case sensitivy.
+	SetKeysCaseSensitive(true)
+	r := strings.NewReader(config)
+	if err := unmarshalReader(r, v.config); err != nil {
+		panic(err)
+	}
+
+	Set("RfD", true)
+	assert.Equal(t, nil, Get("rfd"))
+	assert.Equal(t, true, Get("RfD"))
+	assert.Equal(t, 0, cast.ToInt(Get("abcd")))
+	assert.Equal(t, 1, cast.ToInt(Get("aBcD")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.gh")))
+	assert.Equal(t, 2, cast.ToInt(Get("eF.gH")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.ijk")))
+	assert.Equal(t, 3, cast.ToInt(Get("eF.iJk")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.lm.no")))
+	assert.Equal(t, 4, cast.ToInt(Get("eF.Lm.nO")))
+	assert.Equal(t, 0, cast.ToInt(Get("ef.lm.p.q")))
+	assert.Equal(t, 5, cast.ToInt(Get("eF.Lm.P.Q")))
+
+}
+
 func newViperWithConfigFile(t *testing.T) (*Viper, string, func()) {
 	watchDir, err := ioutil.TempDir("", "")
 	require.Nil(t, err)