The practical design of slender concrete compression members is ususally based on simplified calculation methods. The methods given in e.g. Eurocode 2 (2004) and FIP recommendations (1999) are based on extensive calibrations against accurate second order non-linear analysis. In this analysis, however, the time-dependent effects in concrete were taken into account in a simplified way. Thus, creep was modelled with an extended stress-strain curve for the concrete, whereas shrinkage and strength increase were ignored. In this book the significance of the mentioned simplifications is studied by systematic comparisons with a more accurate analysis, where the time-dependent effects are taken into account in a more fundamental way. The accurate analysis is also used for comparisons with the results of a large number of tests on slender concrete columns. The conclusions are that the simplified way of taking account of the time depend effects is sufficiently accurate as a basis for simplified design methods, and that the accurate analysis - using material models from MC90 and Eurocode 2 - generally gives good agreement with the test results.