Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In the mathematical field of topology, a regular homotopy refers to a special kind of homotopy between immersions of one manifold in another and the homotopy must go through immersions and extend continuously to a homotopy of the tangent bundle. Similar to homotopy classes, one defines two immersions to be in the same regular homotopy class if there exists a regular homotopy between them. Regular homotopy for immersions is similar to isotopy of embeddings: they are both restricted types of homotopies.