The Hague Convention on the Service Abroad of Judicial and Extrajudicial Documents in Civil or Commercial Matters is a multilateral treaty designed to simplify the methods for serving process abroad to assure that defendants sued in foreign jurisdictions receive actual and timely notice of suit and to facilitate proof of service abroad.

This convention is used to serve legal documents filed in the United States to be served in foreign countries that have signed as a signatory.
For example, if you need to serve a Summons and Complaint to a company in China, Germany, Italy, France, Albania, Egypt, and England you would use this method. There are many other countries part of this convention and every year new countries are added.

This method is much simpler and faster than the Letters of Rogatory method. Also, another differentiating factor is that under the Hague Convention the attorney can sign the application versus the Letters of Rogatory that is signed by the Judge presiding over the matter.