. International genetic and genomic evaluations of beef cattle.PhD thesis, Wageningen University, the Netherlands.In cattle, advancements in reproductive technologies such as artificial insemination allowed breeders to access the genetic material of superior bulls from foreign countries. However, animals' estimated breeding values (EBV) computed from different national evaluations are not directly comparable across countries due to differences in scales and genetic bases, trait and model definitions, and the possible presence of genotype-by-environment interactions. International evaluations account for such differences by jointly analysing all national data and modelling the same trait recorded in different countries as different correlated traits. The resulting international EBV (EBV INT ) facilitate the comparison of domestic and foreign sires and worldwide trading of their genetic material. This thesis aimed to improve and further develop methodologies for international beef cattle evaluations (Interbeef) by addressing various challenges, mainly related to: i) the estimation of across-country genetic correlations (r g ) and their impact on the EBV INT ; ii) the inclusion of national genomic information; and iii) the development of an official procedure for participating countries to integrate the distributed EBV INT back into their national evaluations. First, I showed that both large and small participating countries benefit from current Interbeef pedigree-based evaluations. Second, I showed the feasibility of estimating across-country r g using a multi-trait approach that simultaneously fits data from all countries and proposed data sub-setting strategies to improve computational time. Third, I showed that the current practice of assuming across-country direct-maternal r g to be 0 has limited impact on the EBV INT of animals of interest such as publishable sires, i.e., sires that meet Interbeef publications rules. On the other hand, assuming zero within-country direct-maternal r g impacts the EBV INT of such animals. Fourth, I developed international genomic evaluations for beef cattle using a single-step SNPBLUP approach (ssSNPBLUP). International ssSNPBLUP evaluations lead to higher accuracies compared to both current international pedigree evaluations and either national pedigree or genomic evaluations, while keeping similar or slightly reduced level and dispersion bias. Finally, I developed a generalized procedure to integrate pedigree-based or singlestep EBV INT of publishable sires into national evaluations. The procedure can be easily implemented with current software. Compared to national evaluations without integration, the integration reduces level bias, gives similar dispersion, and increases accuracies of publishable sires' EBV INT . Overall, this thesis contributes to the development of international evaluations of beef cattle.