| Synchronous Event Receivers | Asynchronous Event Receivers |
| They are known as ‘Before’ events | They are known as ‘After’ events |
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| Synchronous event receivers are called before the actual event occurs and before SharePoint has written any content in Content Database, that’s why they are called before events | Asynchronous event receivers are called after the actual event occurs and after SharePoint has written content in Content Database, that’s why they are called after events |
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| Events ending with “–ing” are named synchronous events. E.g. Item Adding, Item Deleting | Events ending with “–ed” are named asynchronous events. E.g. Item Added, Item Deleted |
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| Event is executed in the same thread as the triggering action is running. | Event is executed in different thread than the triggering action. |
| You can cancel the running event | You cannot cancel the running event |
| You can get HttpContext | You cannot get HttpContext |
| You can display error message | You cannot display error message |