diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9e8490e2..9e3d3801 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@
 - Add `panic`/`Error.panic`. https://github.com/rescript-association/rescript-core/pull/72
 - The globally available `null` value now originates from `Nullable` and not `Null`, just like the globally available `undefined` value does. https://github.com/rescript-association/rescript-core/pull/88
 - Add `Int.range` and `Int.rangeWithOptions`, https://github.com/rescript-association/rescript-core/pull/52
+- Add `flat`, `expect`, and `or` to `Option`, deprecate `orElse`. https://github.com/rescript-association/rescript-core/pull/57
 
 ### Documentation
 
diff --git a/src/Core__Option.mjs b/src/Core__Option.mjs
index 29ad429b..d0679d4c 100644
--- a/src/Core__Option.mjs
+++ b/src/Core__Option.mjs
@@ -2,6 +2,14 @@
 
 import * as Curry from "rescript/lib/es6/curry.js";
 import * as Caml_option from "rescript/lib/es6/caml_option.js";
+import * as Core__Error from "./Core__Error.mjs";
+
+function flat(opt) {
+  if (opt !== undefined) {
+    return Caml_option.valFromOption(opt);
+  }
+  
+}
 
 function filter(opt, p) {
   var p$1 = Curry.__1(p);
@@ -19,9 +27,9 @@ function forEach(opt, f) {
   
 }
 
-function getExn(x) {
-  if (x !== undefined) {
-    return Caml_option.valFromOption(x);
+function getExn(opt) {
+  if (opt !== undefined) {
+    return Caml_option.valFromOption(opt);
   }
   throw {
         RE_EXN_ID: "Not_found",
@@ -29,6 +37,14 @@ function getExn(x) {
       };
 }
 
+function expect(opt, message) {
+  if (opt !== undefined) {
+    return Caml_option.valFromOption(opt);
+  } else {
+    return Core__Error.panic(message);
+  }
+}
+
 function mapWithDefault(opt, $$default, f) {
   var f$1 = Curry.__1(f);
   if (opt !== undefined) {
@@ -62,7 +78,7 @@ function getWithDefault(opt, $$default) {
   }
 }
 
-function orElse(opt, other) {
+function or(opt, other) {
   if (opt !== undefined) {
     return opt;
   } else {
@@ -70,12 +86,12 @@ function orElse(opt, other) {
   }
 }
 
-function isSome(x) {
-  return x !== undefined;
+function isSome(opt) {
+  return opt !== undefined;
 }
 
-function isNone(x) {
-  return x === undefined;
+function isNone(opt) {
+  return opt === undefined;
 }
 
 function eq(a, b, f) {
@@ -106,14 +122,19 @@ function cmp(a, b, f) {
   }
 }
 
+var orElse = or;
+
 export {
+  flat ,
   filter ,
   forEach ,
   getExn ,
+  expect ,
   mapWithDefault ,
   map ,
   flatMap ,
   getWithDefault ,
+  or ,
   orElse ,
   isSome ,
   isNone ,
diff --git a/src/Core__Option.res b/src/Core__Option.res
index 9b688647..726a074f 100644
--- a/src/Core__Option.res
+++ b/src/Core__Option.res
@@ -22,73 +22,83 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
 
+let flat = opt =>
+  switch opt {
+  | Some(v) => v
+  | None => None
+  }
+
 let filterU = (opt, p) =>
   switch opt {
-  | Some(x) as some if p(. x) => some
+  | Some(value) as some if p(. value) => some
   | _ => None
   }
 
-let filter = (opt, p) => filterU(opt, (. x) => p(x))
+let filter = (opt, p) => filterU(opt, (. value) => p(value))
 
 let forEachU = (opt, f) =>
   switch opt {
-  | Some(x) => f(. x)
+  | Some(value) => f(. value)
   | None => ()
   }
 
-let forEach = (opt, f) => forEachU(opt, (. x) => f(x))
+let forEach = (opt, f) => forEachU(opt, (. value) => f(value))
 
-let getExn = x =>
-  switch x {
-  | Some(x) => x
+let getExn = opt =>
+  switch opt {
+  | Some(value) => value
   | None => raise(Not_found)
   }
 
+let expect = (opt, message) =>
+  switch opt {
+  | Some(value) => value
+  | None => Core__Error.panic(message)
+  }
+
 external getUnsafe: option<'a> => 'a = "%identity"
 
 let mapWithDefaultU = (opt, default, f) =>
   switch opt {
-  | Some(x) => f(. x)
+  | Some(value) => f(. value)
   | None => default
   }
 
-let mapWithDefault = (opt, default, f) => mapWithDefaultU(opt, default, (. x) => f(x))
+let mapWithDefault = (opt, default, f) => mapWithDefaultU(opt, default, (. value) => f(value))
 
 let mapU = (opt, f) =>
   switch opt {
-  | Some(x) => Some(f(. x))
+  | Some(value) => Some(f(. value))
   | None => None
   }
 
-let map = (opt, f) => mapU(opt, (. x) => f(x))
+let map = (opt, f) => mapU(opt, (. value) => f(value))
 
 let flatMapU = (opt, f) =>
   switch opt {
-  | Some(x) => f(. x)
+  | Some(value) => f(. value)
   | None => None
   }
 
-let flatMap = (opt, f) => flatMapU(opt, (. x) => f(x))
+let flatMap = (opt, f) => flatMapU(opt, (. value) => f(value))
 
 let getWithDefault = (opt, default) =>
   switch opt {
-  | Some(x) => x
+  | Some(value) => value
   | None => default
   }
 
-let orElse = (opt, other) =>
+let or = (opt, other) =>
   switch opt {
-  | Some(_) as some => some
+  | Some(_) => opt
   | None => other
   }
 
-let isSome = x =>
-  switch x {
-  | Some(_) => true
-  | None => false
-  }
+let orElse = or
+
+let isSome = opt => opt !== None
 
-let isNone = x => x == None
+let isNone = opt => opt == None
 
 let eqU = (a, b, f) =>
   switch a {
diff --git a/src/Core__Option.resi b/src/Core__Option.resi
index fb3c8a46..2c1f2025 100644
--- a/src/Core__Option.resi
+++ b/src/Core__Option.resi
@@ -39,6 +39,18 @@ let someString: option<string> = Some("hello")
 ```
 */
 
+/**
+`flat(value)` flattens a nested `option` value to a single level.
+
+## Examples
+
+```rescript
+Option.flat(Some(Some(10))) // Some(10)
+Option.flat(Some(None)) // None
+```
+*/
+let flat: option<option<'a>> => option<'a>
+
 /**
 `filter(opt, f)` applies `f` to `opt`, if `f` returns `true`, then it returns `Some(value)`, otherwise returns `None`.
 
@@ -66,7 +78,7 @@ Option.forEach(None, x => Console.log(x)) // returns ()
 let forEach: (option<'a>, 'a => unit) => unit
 
 /**
-`getExn(opt)` returns `value` if `opt` is `Some(value)`, otherwise raises an exception.
+`getExn(opt)` returns `value` if `opt` is `Some(value)`, raises `Not_found` if `None`.
 
 ```rescript
 Option.getExn(Some(3)) // 3
@@ -75,10 +87,24 @@ Option.getExn(None) /* Raises an Error */
 
 ## Exceptions
 
-- Raises an error if `opt` is `None`
+- Raises `Not_found` if `opt` is `None`
 */
 let getExn: option<'a> => 'a
 
+/**
+`expect(opt, message)` returns `value` if `Some(value)`, raises a `Failure` expection with the given message if `None`.
+
+```rescript
+Option.expect(Some(3), "should not be None") // 3
+Option.expect(None, "should not be None") // Raises `Failure("should not be None")`
+```
+
+## Exceptions
+
+- Panics if `opt` is `None`
+*/
+let expect: (option<'a>, string) => 'a
+
 /**
 `getUnsafe(value)` returns `value`.
 
@@ -89,9 +115,9 @@ Option.getUnsafe(Some(3)) == 3
 Option.getUnsafe(None) // Raises an error
 ```
 
-## Exceptions
+## Important
 
-- This is an unsafe operation, it assumes `value` is neither `None` nor `Some(None(...)))`
+This is an unsafe operation, it assumes `value` is neither `None`, `Some(None))`, `Some(Some(None))` etc.
 */
 external getUnsafe: option<'a> => 'a = "%identity"
 
@@ -160,6 +186,19 @@ None->greet // "Greetings Anonymous"
 */
 let getWithDefault: (option<'a>, 'a) => 'a
 
+/**
+`or(opt1, opt2)` returns `opt2` if `opt1` is `None`, otherwise `opt1`.
+
+## Examples
+
+```rescript
+Option.or(Some(1812), Some(1066)) == Some(1812)
+Option.or(None, Some(1066) == Some(1066)
+Option.or(None, None) == None
+```
+*/
+let or: (option<'a>, option<'a>) => option<'a>
+
 /**
 `orElse(opt1, opt2)` returns `opt2` if `opt1` is `None`, otherwise `opt1`.
 
@@ -171,6 +210,7 @@ Option.orElse(None, Some(1066) == Some(1066)
 Option.orElse(None, None) == None
 ```
 */
+@deprecated("Use `or` instead")
 let orElse: (option<'a>, option<'a>) => option<'a>
 
 /**