In this paper, we describe a multilingual open-source computational grammar of Persian, developed in Grammatical Framework (GF) ― A type-theoretical grammar formalism. We discuss in detail the structure of different syntactic (i.e. noun phrases, verb phrases, adjectival phrases, etc.) categories of Persian. First, we show how to structure and construct these categories individually. Then we describe how they are glued together to make well-formed sentences in Persian, while maintaining the grammatical features such as agreement, word order, etc. We also show how some of the distinctive features of Persian, such as the ezafe construction, are implemented in GF. In order to evaluate the grammar's correctness, and to demonstrate its usefulness, we have added support for Persian in a multilingual application grammar (the Tourist Phrasebook) using the reported resource grammar.