diff --git a/isocode.go b/isocode.go
index 4e24951..e43c6e2 100644
--- a/isocode.go
+++ b/isocode.go
@@ -16,6 +16,8 @@
 
 package lingua
 
+import "strings"
+
 // IsoCode639_1 is the type used for enumerating the ISO 639-1 code
 // representations of the supported languages.
 //
@@ -487,3 +489,19 @@ const (
 	// UnknownIsoCode639_3 is the ISO 639-3 code for Unknown.
 	UnknownIsoCode639_3
 )
+
+var stringToIsoCode639_1 = func() map[string]IsoCode639_1 {
+	m := make(map[string]IsoCode639_1)
+	for isoCode := AF; isoCode <= ZU; isoCode++ {
+		m[strings.ToLower(isoCode.String())] = isoCode
+	}
+	return m
+}()
+
+var stringToIsoCode639_3 = func() map[string]IsoCode639_3 {
+	m := make(map[string]IsoCode639_3)
+	for isoCode := AFR; isoCode <= ZUL; isoCode++ {
+		m[strings.ToLower(isoCode.String())] = isoCode
+	}
+	return m
+}()
diff --git a/language.go b/language.go
index deb21cc..06e60a6 100644
--- a/language.go
+++ b/language.go
@@ -16,6 +16,8 @@
 
 package lingua
 
+import "strings"
+
 // Language is the type used for enumerating the so far 75 languages which can
 // be detected by Lingua.
 //
@@ -146,25 +148,43 @@ func AllLanguagesWithLatinScript() []Language {
 }
 
 // GetLanguageFromIsoCode639_1 returns the language for the given
-// ISO 639-1 code.
+// ISO 639-1 code enum value.
 func GetLanguageFromIsoCode639_1(isoCode IsoCode639_1) Language {
 	for _, language := range AllLanguages() {
 		if language.IsoCode639_1() == isoCode {
 			return language
 		}
 	}
-	return -1
+	return Unknown
+}
+
+// GetLanguageFromIsoCode639_1String returns the language for the given
+// ISO 639-1 code string value.
+func GetLanguageFromIsoCode639_1String(isoCode string) Language {
+	if isoCodeEnum, ok := stringToIsoCode639_1[strings.ToLower(isoCode)]; ok {
+		return GetLanguageFromIsoCode639_1(isoCodeEnum)
+	}
+	return Unknown
 }
 
 // GetLanguageFromIsoCode639_3 returns the language for the given
-// ISO 639-3 code.
+// ISO 639-3 code enum value.
 func GetLanguageFromIsoCode639_3(isoCode IsoCode639_3) Language {
 	for _, language := range AllLanguages() {
 		if language.IsoCode639_3() == isoCode {
 			return language
 		}
 	}
-	return -1
+	return Unknown
+}
+
+// GetLanguageFromIsoCode639_3String returns the language for the given
+// ISO 639-3 code string value.
+func GetLanguageFromIsoCode639_3String(isoCode string) Language {
+	if isoCodeEnum, ok := stringToIsoCode639_3[strings.ToLower(isoCode)]; ok {
+		return GetLanguageFromIsoCode639_3(isoCodeEnum)
+	}
+	return Unknown
 }
 
 func allLanguagesWithScript(script alphabet) (languages []Language) {
diff --git a/language_test.go b/language_test.go
index 28ce64e..0f36213 100644
--- a/language_test.go
+++ b/language_test.go
@@ -259,3 +259,33 @@ func TestAllLanguagesWithLatinScript(t *testing.T) {
 		},
 		AllLanguagesWithLatinScript())
 }
+
+func TestGetLanguageFromIsoCode639_1(t *testing.T) {
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_1(AF))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_1(ZU))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_1(UnknownIsoCode639_1))
+}
+
+func TestGetLanguageFromIsoCode639_1String(t *testing.T) {
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_1String("AF"))
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_1String("af"))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_1String("ZU"))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_1String("zu"))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_1String("afr"))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_1String("xy"))
+}
+
+func TestGetLanguageFromIsoCode639_3(t *testing.T) {
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_3(AFR))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_3(ZUL))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_3(UnknownIsoCode639_3))
+}
+
+func TestGetLanguageFromIsoCode639_3String(t *testing.T) {
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_3String("AFR"))
+	assert.Equal(t, Afrikaans, GetLanguageFromIsoCode639_3String("afr"))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_3String("ZUL"))
+	assert.Equal(t, Zulu, GetLanguageFromIsoCode639_3String("zul"))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_3String("af"))
+	assert.Equal(t, Unknown, GetLanguageFromIsoCode639_3String("xyz"))
+}