Technical Abstract: Lentil plants encounter numerous diseases that are caused by fungi, viruses and nematodes. Diseases not only affect plant growth and reduce yield, but also infect seeds reducing grain quality and grading, which affect market price, and transmit diseases if the grain seeds are used for planting. This article reviews some of the important lentil diseases, including Ascochyta blight, Botrytis gray mold, rust, Fusarium wilt, anthracnose, and powdery mildew. Ascochyta blight is a foliar disease caused by the fungus Ascochyta lentis, which is specific for lentil. Botrytis gray mold of lentil is found worldwide in all lentil production regions, and is caused by Botrytis cinerea and occasionally also caused by Botrytis fabae. Rust of lentil is caused by the autoecious fungus Uromyces viciae-fabae. The pathogen can complete its life cycle on lentil plant without an alternating host. Fusarium wilt of lentil, a wide spread disease, is caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. lentil, which infects only lentil. Anthracnose caused by the fungus Colletotrichum truncatum is an economically important disease in western Canada and many other countries. Anthracnose refers to disease lesions that are sunken and necrotic, and with a defined black margin. Powdery mildew of lentil, caused by Erysiphe trifolii in North America, is an important disease in the greenhouse. The disease may devastate valuable breeding materials such as F1 plants. With lentil production expanding to areas where lentil has not been previously cultivated and with climate change, less important diseases may become important and new diseases may emerge. Research efforts need to be directed to those less-known diseases to gain a more complete understanding of the impact of diseases on lentil production.