Lentil (Lens culinaris Medik.) is an important cool-season legume that can be severely damaged by rust (Uromyces viciae-fabae (Pers.) Schröt.) in many parts of the world. In this work, a collection of L. culinaris germplasm accessions was screened under growth chamber conditions for response to U. viciae-fabae. Several sources of incomplete resistance have been identified, both of hypersensitive and of non-hypersensitive nature. Incomplete hypersensitive resistance was due to a late-acting host cell necrosis that resulted in an intermediate infection type (IT). Incomplete non-hypersensitive resistance was due to a hampered cell penetration not associated with host cell necrosis, reducing the number of haustoria per colony and therefore hindering the growth of the colony and reducing and retarding disease development in spite of a high IT.