diff --git a/src/collections_me.c b/src/collections_me.c
index 72d46dc..49e128c 100644
--- a/src/collections_me.c
+++ b/src/collections_me.c
@@ -166,6 +166,7 @@ const zend_function_entry collection_methods[] = {
     PHP_ME(Collection, isNotEmpty, NULL, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, keys, NULL, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, last, predicate_arginfo, ZEND_ACC_PUBLIC)
+    PHP_ME(Collection, lastIndexOf, element_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, map, transform_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, mapKeys, transform_arginfo, ZEND_ACC_PUBLIC)
     PHP_ME(Collection, mapKeysTo, destination_transform_arginfo, ZEND_ACC_PUBLIC)
diff --git a/src/collections_methods.c b/src/collections_methods.c
index c711482..44ff5d0 100644
--- a/src/collections_methods.c
+++ b/src/collections_methods.c
@@ -872,17 +872,62 @@ PHP_METHOD(Collection, groupByTo)
 
 PHP_METHOD(Collection, indexOf)
 {
-    
+    zval* element;
+    ZEND_PARSE_PARAMETERS_START(1, 1)
+        Z_PARAM_ZVAL(element)
+    ZEND_PARSE_PARAMETERS_END();
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    INIT_EQUAL_CHECK_FUNC(element);
+    ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
+        if (equal_check_func(element, &bucket->val)) {
+            if (bucket->key)
+                RETURN_STR(bucket->key);
+            RETURN_LONG(bucket->h);
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NULL();
 }
 
 PHP_METHOD(Collection, indexOfFirst)
 {
-    
+    zend_fcall_info fci;
+    zend_fcall_info_cache fcc;
+    ZEND_PARSE_PARAMETERS_START(1, 1)
+        Z_PARAM_FUNC(fci, fcc)
+    ZEND_PARSE_PARAMETERS_END();
+    INIT_FCI(1);
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    ZEND_HASH_FOREACH_BUCKET(current, Bucket* bucket)
+        ZVAL_COPY_VALUE(&params[0], &bucket->val);
+        zend_call_function(&fci, &fcc);
+        if (zend_is_true(&retval)) {
+            if (bucket->key)
+                RETURN_STR(bucket->key);
+            RETURN_LONG(bucket->h);
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NULL();
 }
 
 PHP_METHOD(Collection, indexOfLast)
 {
-    
+    zend_fcall_info fci;
+    zend_fcall_info_cache fcc;
+    ZEND_PARSE_PARAMETERS_START(1, 1)
+        Z_PARAM_FUNC(fci, fcc)
+    ZEND_PARSE_PARAMETERS_END();
+    INIT_FCI(1);
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    ZEND_HASH_REVERSE_FOREACH_BUCKET(current, Bucket* bucket)
+        ZVAL_COPY_VALUE(&params[0], &bucket->val);
+        zend_call_function(&fci, &fcc);
+        if (zend_is_true(&retval)) {
+            if (bucket->key)
+                RETURN_STR(bucket->key);
+            RETURN_LONG(bucket->h);
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NULL();
 }
 
 PHP_METHOD(Collection, init)
@@ -958,6 +1003,24 @@ PHP_METHOD(Collection, last)
     RETVAL_NULL();
 }
 
+PHP_METHOD(Collection, lastIndexOf)
+{
+    zval* element;
+    ZEND_PARSE_PARAMETERS_START(1, 1)
+        Z_PARAM_ZVAL(element)
+    ZEND_PARSE_PARAMETERS_END();
+    zend_array* current = COLLECTION_FETCH_CURRENT();
+    INIT_EQUAL_CHECK_FUNC(element);
+    ZEND_HASH_REVERSE_FOREACH_BUCKET(current, Bucket* bucket)
+        if (equal_check_func(element, &bucket->val)) {
+            if (bucket->key)
+                RETURN_STR(bucket->key);
+            RETURN_LONG(bucket->h);
+        }
+    ZEND_HASH_FOREACH_END();
+    RETVAL_NULL();
+}
+
 PHP_METHOD(Collection, map)
 {
     
@@ -1361,7 +1424,7 @@ PHP_METHOD(Collection, slice)
 
 PHP_METHOD(Collection, sort)
 {
-    
+
 }
 
 PHP_METHOD(Collection, sortBy)
diff --git a/src/php_collections_me.h b/src/php_collections_me.h
index bb85252..ade62c4 100644
--- a/src/php_collections_me.h
+++ b/src/php_collections_me.h
@@ -52,6 +52,7 @@ PHP_METHOD(Collection, isEmpty);
 PHP_METHOD(Collection, isNotEmpty);
 PHP_METHOD(Collection, keys);
 PHP_METHOD(Collection, last);
+PHP_METHOD(Collection, lastIndexOf);
 PHP_METHOD(Collection, map);
 PHP_METHOD(Collection, mapKeys);
 PHP_METHOD(Collection, mapKeysTo);
diff --git a/stubs/Collection.php b/stubs/Collection.php
index 1d2d3e1..1fd06a7 100644
--- a/stubs/Collection.php
+++ b/stubs/Collection.php
@@ -389,6 +389,14 @@ class Collection implements ArrayAccess, Countable
      */
     function last($predicate) {}
 
+    /**
+     * Returns last key of element, or null if the collection does not contain element.
+     *
+     * @param mixed $element
+     * @return int|string|null
+     */
+    function lastIndexOf($element) {}
+
     /**
      * Returns a collection containing the results of applying the given transform function
      * to each element in the original collection.
diff --git a/tests/035-index-of.phpt b/tests/035-index-of.phpt
new file mode 100644
index 0000000..a99db7b
--- /dev/null
+++ b/tests/035-index-of.phpt
@@ -0,0 +1,23 @@
+--TEST--
+Test Collection::indexOf(), Collection::lastIndexOf(), Collection::indexOfFirst(), Collection::indexOfLast().
+--FILE--
+<?php
+$collection = Collection::init(['t', 'B', 13, 'f', 'G', 19, 'N', 'f']);
+$first_f_at = $collection->indexOf('f');
+if ($first_f_at != 3)
+    echo 'Collection::indexOf() failed.', PHP_EOL;
+$last_f_at = $collection->lastIndexOf('f');
+if ($last_f_at != 7)
+    echo 'Collection::lastIndexOf() failed.', PHP_EOL;
+$first_numeric_at = $collection->indexOfFirst(function ($value) {
+    return is_numeric($value);
+});
+if ($first_numeric_at != 2)
+    echo 'Collection::indexOfFirst() failed.', PHP_EOL;
+$last_upper_case_at = $collection->indexOfLast(function ($value) {
+    return ctype_upper($value);
+});
+if ($last_upper_case_at != 6)
+    echo 'Collection::indexOfLast() failed.', PHP_EOL;
+?>
+--EXPECT--