Theoretical studies on the effects of linkage on variability of quantitative traits and response to directional selection in finite populations are reviewed. Emphasis is given to predictions that can be based on observable parameters, such as population size, chromosome lengths and the increment in variance from new mutations. Although truncation selection produces negative linkage disequilibrium in infinite populations, simulation results show that the effects of linkage on response are more pronounced in finite populations. Substantial linkage disequilibrium at the DNA sequence level is being found in population surveys. Some of the results and their interpretation are discussed.