These historic creeds and confessions are known as the Three Forms of Unity.
The Heidelberg Catechism is a document written in a question-and-answer format to help explain biblical teaching to children and those new and old to the faith.
The Belgic Confession explains various biblical teachings. This confession stands as one of the best symbolical statements of Reformed doctrine.
The Canons of Dort are series of technical responses to specific theological issues such as the nature and extent of sin, election, atonement, grace, and justification.