Mr. Ralf Hussmanns (ILO) in his paper on ‘Issues Relating to the International Definition of the Informal Sector and their Impact on the International Comparability of Informal Sector Statistics’ presented salient features of the definition adopted by the 15^th ICLS concerning statistics of employment in the informal sector. It was emphasised that some elements of flexibility in the definition of the informal sector were intentional because the resolution was the first international recommendation ever adopted on the subject and its main purpose was to provide technical guidelines for the development of the informal sector statistics rather than enforcing international comparability of data. The review of the international practices in the collection of statistical data on the informal sector, presented in the paper, clearly brings out that there are currently some problems in using these data for international comparison. Some of the factors responsible for data comparability problems were noted to be differences in the data sources, differences in the geographical coverage of surveys, differences in the kinds of economic activities covered, non use of criteria of legal organisation and lack of complete set of accounts, differences in criteria used to define the informal sector, differences in the way that these criteria are specified, differences in the treatment of specific groups of enterprises or workers and inclusion or exclusion of persons who have a secondary job in the informal sector but have the main job outside the informal sector etc. Now that more and more countries have started collecting and publishing data on employment and other characteristics of the informal sector or closely related concepts such as the unorganised sector, micro and small enterprises, household economic activities or unregistered employment; there is a demand to harmonise, as far as possible, the informal sector definitions used by the countries concerned for the purpose of improving the international comparability.