The virulent plasmid pYV encodes Yersinia adhesin A (YadA) and the Yersinia outer protein (Yop) virulon, a system consisting of secreted proteins called Yops and their dedicated type III secretion system (T3SS) apparatus called Ysc. Yersinia is a genus of Gram-negative, rod-shaped, facultative anaerobes in the family Enterobacteriaceae. With the help of the mouse model, the yersinia T3SS has been studied in detail using molecular, cellular, genetic, and biochemical techniques, yielding insight into the efficiency and sophistication of the complex. Temperature is a key environmental clue for the expression of yersinia genes. Rabbits have been a suitable and reproducible animal model to examine the course of intestinal Yersinia infection. In mouse model, diarrhea is not a major symptom. Application of molecular, cellular, genetic, and biochemical techniques in combination with in vitro models yielded valuable insights into efficiency and sophistication of the Yersinia T3SS.