This thesis deals with the evaluation of measurements of water vapor transport and sorption in wood. It mainly concerns measurements of the weight response of a sample after a step change in relative humidity. The thesis consists of an introduction and eight papers. The eight papers have the following contents: 1. A description of the instrumentation and its performance characteristics. 2. Some first results on sorption in spruce wood. Non-Fiction behavior is seen above 75% relative humidity. 3. In this part the main experimental results are presented. At lower relative humidity (absorption from 54 to 75%) the normally used Fiction approach can describe the major part of the sorption process. At higher relative humidity (from 75 to 84%), however, the major part of the sorption is very slow and governed by non-Fiction effects, which are not dependent on direction of flow, sample size or wood species. The slow sorption of water vapor in the cell wall is believed to cause this phenomenon. 4. A test of the effect of different disturbances (e.g. the surface resistance) on the normally used methods of evaluating sorption measurements is presented. 5. In this paper problems concerning measurements of surface mass transfer coefficients are discussed. 6. A discussion of how non-Fickian behavior in wood could be measured and modelled. 7. An error analysis of a transient sorption measurement is developed. 8. The error analysis is applied on two measurements.