We construct a nerve from double categories into double (∞, 1)-categories and show that it gives a right Quillen and homotopically fully faithful functor between the model structure for weakly horizontally invariant double categories and the model structure on bisimplicial spaces for double (∞, 1)-categories seen as double Segal objects in spaces complete in the horizontal direction. We then restrict the nerve along a homotopical horizontal embedding of 2-categories into double categories, and show that it gives a right Quillen and homotopically fully faithful functor between Lack's model structure for 2-categories and the model structure for 2-fold complete Segal spaces. We further show that Lack's model structure is right-induced along this nerve from the model structure for 2-fold complete Segal spaces. Contents 1. Introduction 1.1. Outline Acknowledgments 2. Preliminaries on 2-dimensional categories 2.1. 2-categories, double categories, and their relations 2.2. Notions of equivalences in a double category 3. Model structures on 2Cat and DblCat 3.1. Lack's model structure for 2-categories 3.2. Model structure for weakly horizontally invariant double categories 4. Model structures for (∞, 2)-categories and double (∞, 1)-categories 4.1. Model structures for double (∞, 1)-categories 4.2. Model structure for 2-fold complete Segal spaces 5. Nerve of double categories 5.1. Definition of the nerve 5.2. The nerve N is right Quillen 5.3. The nerve N is homotopically fully faithful 5.4. Level of fibrancy of nerves of double categories 6. Nerve of 2-categories 6.1. The nerve NH ≃ is right Quillen and homotopically fully faithful 6.2. 2Cat is right-induced from 2CSS along NH ≃ 6.3. Comparison between the nerves NH and NH ≃ Appendix A. Weakly horizontally invertible squares A.1. Unique inverse lemma A.2. Weakly horizontally invertible square in HA, H ≃ A, and L ≃ A A.3. Horizontal pseudo-natural equivalences Appendix B. Explicit description of the nerves in lower dimensions B.1. Nerve of a double category B.2. Nerve of a 2-category B.3. Nerve of a horizontal double category References