The susceptibility of Brassica napus L. to increased temperatures within western Canada requires attention if we hope to minimize the negative impact of heat stress on this key commodity. The objective of this research was to discover, access and determine methods to improve thermotolerance in B. napus. The first research project was constructed to assess if variation to heat stress exists within the primary B. napus gene pool. This was done using 10 B. napus inbreds which were grown in greenhouses and placed in growth chambers to simulate heat stress conditions during floral development and flowering. Significant variation existed within the germplasm screened, with five inbreds classified as heat tolerant and four as heat susceptible. The second project investigated the effect of heterosis on heat stress in B. napus. Ten inbreds from the first project and 25 hybrids created from these inbreds were used to compare the response of the inbreds and hybrids to increased temperatures evaluated in field environments across four site years. The potential for heterosis to minimize the impact of the high temperature was apparent given the 25 % reduction in seed yield for the inbreds, while the hybrid seed yield was reduced by 20 % under heat stress. The final project utilized a doubled haploid population created from an F1 donor produced from a cross between heat tolerant and heat susceptible B. napus inbred parents. This population was evaluated in an average and high temperature field environment across three site years. Genotypic data were generated and used to create a linkage map for QTL analysis, and to assess the viability of using whole genome predictions to select for heat tolerance. There were 66 QTL identified for nine traits with a single putative QTL for yield discovered within the high temperature environment alone. The whole genome prediction accuracies ranged from 0.14 – 0.66 and differed across treatments. Research findings provide evidence of variation to high temperature stress within B. napus and indicate continued screening of germplasm within high temperature environments will enable genetic gain for heat tolerance.