Integrins mediate cell adhesion, permit traction forces important for cell migration, and cross-talk with growth factor receptors to regulate cell proliferation, cell survival, and cell differentiation. The plethora of functions explains their central role for development and disease. The progress in mouse genetics and the ease with which the mouse genome can be manipulated enormously contributed to our understanding of how integrins exert their functions at the molecular level. In the present chapter, we describe tests that are routinely used in our laboratory to investigate embryos, organs, and cells (peri-implantation embryos, hematopoietic system, epidermis, and hair follicles) that lack the expression of integrins or integrin-associated proteins.