diff --git a/.gitignore b/.gitignore
index 01b5c44..e066e2c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -27,3 +27,4 @@ _testmain.go
 
 # exclude dependencies in the `/vendor` folder
 vendor
+.idea/
diff --git a/viper.go b/viper.go
index 1875627..b39d350 100644
--- a/viper.go
+++ b/viper.go
@@ -203,6 +203,7 @@ type Viper struct {
 	properties *properties.Properties
 
 	onConfigChange func(fsnotify.Event)
+	caseSensitive  bool
 }
 
 // New returns an initialized Viper instance.
@@ -219,6 +220,7 @@ func New() *Viper {
 	v.env = make(map[string]string)
 	v.aliases = make(map[string]string)
 	v.typeByDefValue = false
+	v.caseSensitive = false
 
 	return v
 }
@@ -277,6 +279,13 @@ func (v *Viper) OnConfigChange(run func(in fsnotify.Event)) {
 	v.onConfigChange = run
 }
 
+func SetCaseSensitive(flag bool) {
+	v.SetCaseSensitive(flag)
+}
+func (v *Viper) SetCaseSensitive(flag bool) {
+	v.caseSensitive = flag
+}
+
 func WatchConfig() { v.WatchConfig() }
 
 func (v *Viper) WatchConfig() {
@@ -536,7 +545,7 @@ 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.properCase(strings.Join(path[0:i], v.keyDelim))
 
 		next, ok := source[prefixKey]
 		if ok {
@@ -665,7 +674,7 @@ func GetViper() *Viper {
 // Get returns an interface. For a specific value use one of the Get____ methods.
 func Get(key string) interface{} { return v.Get(key) }
 func (v *Viper) Get(key string) interface{} {
-	lcaseKey := strings.ToLower(key)
+	lcaseKey := v.properCase(key)
 	val := v.find(lcaseKey)
 	if val == nil {
 		return nil
@@ -918,7 +927,7 @@ 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.properCase(key)] = flag
 	return nil
 }
 
@@ -933,7 +942,7 @@ func (v *Viper) BindEnv(input ...string) error {
 		return fmt.Errorf("BindEnv missing key to bind to")
 	}
 
-	key = strings.ToLower(input[0])
+	key = v.properCase(input[0])
 
 	if len(input) == 1 {
 		envkey = v.mergeWithEnvPrefix(key)
@@ -1083,7 +1092,7 @@ func readAsCSV(val string) ([]string, error) {
 // IsSet is case-insensitive for a key.
 func IsSet(key string) bool { return v.IsSet(key) }
 func (v *Viper) IsSet(key string) bool {
-	lcaseKey := strings.ToLower(key)
+	lcaseKey := v.properCase(key)
 	val := v.find(lcaseKey)
 	return val != nil
 }
@@ -1107,11 +1116,11 @@ func (v *Viper) SetEnvKeyReplacer(r *strings.Replacer) {
 // This enables one to change a name without breaking the application
 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.properCase(key))
 }
 
 func (v *Viper) registerAlias(alias string, key string) {
-	alias = strings.ToLower(alias)
+	alias = v.properCase(alias)
 	if alias != key && alias != v.realKey(key) {
 		_, exists := v.aliases[alias]
 
@@ -1167,11 +1176,14 @@ func (v *Viper) InConfig(key string) bool {
 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.properCase(key))
+
+	if !v.caseSensitive {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.properCase(path[len(path)-1])
 	deepestMap := deepSearch(v.defaults, path[0:len(path)-1])
 
 	// set innermost value
@@ -1185,11 +1197,14 @@ func (v *Viper) SetDefault(key string, value interface{}) {
 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.properCase(key))
+
+	if !v.caseSensitive {
+		value = toCaseInsensitiveValue(value)
+	}
 
 	path := strings.Split(key, v.keyDelim)
-	lastKey := strings.ToLower(path[len(path)-1])
+	lastKey := v.properCase(path[len(path)-1])
 	deepestMap := deepSearch(v.override, path[0:len(path)-1])
 
 	// set innermost value
@@ -1342,7 +1357,7 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 	buf := new(bytes.Buffer)
 	buf.ReadFrom(in)
 
-	switch strings.ToLower(v.getConfigType()) {
+	switch v.properCase(v.getConfigType()) {
 	case "yaml", "yml":
 		if err := yaml.Unmarshal(buf.Bytes(), &c); err != nil {
 			return ConfigParseError{err}
@@ -1382,13 +1397,17 @@ 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.properCase(path[len(path)-1])
 			deepestMap := deepSearch(c, path[0:len(path)-1])
 			// set innermost value
 			deepestMap[lastKey] = value
 		}
 	}
 
+	if v.caseSensitive {
+		return nil
+	}
+
 	insensitiviseMap(c)
 	return nil
 }
@@ -1460,9 +1479,9 @@ func (v *Viper) marshalWriter(f afero.File, configType string) error {
 }
 
 func keyExists(k string, m map[string]interface{}) string {
-	lk := strings.ToLower(k)
+	lk := v.properCase(k)
 	for mk := range m {
-		lmk := strings.ToLower(mk)
+		lmk := v.properCase(mk)
 		if lmk == lk {
 			return mk
 		}
@@ -1572,6 +1591,10 @@ func (v *Viper) WatchRemoteConfigOnChannel() error {
 }
 
 func (v *Viper) insensitiviseMaps() {
+	if v.caseSensitive {
+		return
+	}
+
 	insensitiviseMap(v.config)
 	insensitiviseMap(v.defaults)
 	insensitiviseMap(v.override)
@@ -1693,7 +1716,7 @@ 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.properCase(fullKey)] = true
 			continue
 		}
 		// recursively merge to shadow map
@@ -1719,7 +1742,7 @@ outer:
 			}
 		}
 		// add key
-		shadow[strings.ToLower(k)] = true
+		shadow[v.properCase(k)] = true
 	}
 	return shadow
 }
@@ -1737,7 +1760,7 @@ func (v *Viper) AllSettings() map[string]interface{} {
 			continue
 		}
 		path := strings.Split(k, v.keyDelim)
-		lastKey := strings.ToLower(path[len(path)-1])
+		lastKey := v.properCase(path[len(path)-1])
 		deepestMap := deepSearch(m, path[0:len(path)-1])
 		// set innermost value
 		deepestMap[lastKey] = value
@@ -1827,6 +1850,14 @@ func (v *Viper) findConfigFile() (string, error) {
 	return "", ConfigFileNotFoundError{v.configName, fmt.Sprintf("%s", v.configPaths)}
 }
 
+func (v *Viper) properCase(s string) string {
+	if !v.caseSensitive {
+		s = strings.ToLower(s)
+	}
+
+	return s
+}
+
 // Debug prints all configuration registries for debugging
 // purposes.
 func Debug() { v.Debug() }