This Manual is an aid to demographers and population experts to appraise the reliability of population data. It overviews the factors determining the quality of data on population size, age and sex distributions and migrations derived from censuses, surveys, vital registration and other sources of data. The Manual presents methods for appraising completeness, accuracy and consistency of data from these sources. Manual II is closely related to the indirect techniques for demographic estimations presented in the Manuals I, IV and X.