Lentil is an important pulse crop in Saskatchewan. Weed control is central to lentil production due its poor competitive ability and the few herbicide options for use on conventional varieties. Imidazolinone tolerant lentil varieties have been developed to improve herbicidal weed control and crop safety. Two studies were conducted in 2006 and 2007 in Saskatchewan with the research objective of determining the optimal weed control timing and herbicide to maximize weed control and lentil yield. The first experiment investigated the critical period of weed control (CPWC) for lentil. The CPWC was realized by investigating two components; the duration of weed interference and the duration of the weed-free period which respectively determine the beginning and end of the CPWC. The crop remained weedy or weed-free from zero to eleven lentil nodes to investigate the durations of weed interference and weed-free period. There was an inverse relationship between weed biomass and lentil yield such that lentil yield was highest when weed biomass was minimal. The CPWC was found to commence at the five node stage and continue to the ten node stage. The second experiment investigated imazethapyr / imazamox, imazamox and metribuzin + sethoxydim applied at two application times to determine the best herbicide for the CPWC. The results indicated that imazethapyr / imazamox and imazamox applied at the six node stage resulted in the overall lowest weed biomass and highest lentil yield compared to application at the two node stage. In accordance with these results and the CPWC, imazethapyr / imazamox or imazamox should be applied at or before the five to six node stage to maximize lentil yield and minimize weed biomass.