Constructors (được gọi là hàm khởi tạo) là những hàm đặc biệt cho phép thực thi, điều khiển chương trình ngay khi khởi tạo đối tượng. Trong C#, Constructors có tên giống như tên của [Class] và không có giá trị trả về.

In object-oriented programming, a constructor (sometimes shortened to ctor) in a class is a special type of subroutine called to create an object. It prepares the new object for use, often accepting parameters that the constructor uses to set member variables required.

A constructor resembles an instance method, but it differs from a method in that it has no explicit return type, it is not implicitly inherited and it usually has different rules for scope modifiers. Constructors often have the same name as the declaring class. They have the task of initializing the object's data members and of establishing the invariant of the class, failing if the invariant is invalid. A properly written constructor leaves the resulting object in a valid state. Immutable objects must be initialized in a constructor.

Programmers also use the term constructor to denote one of the tags that wraps data in an algebraic data type. This is a different usage than in this article.

Most languages allow overloading the constructor in that there can be more than one constructor for a class, with differing parameters. Some languages take consideration of some special types of constructors.