The Netherlands Postal and Telecommunications Services are using market research Inter alia regarding the telephone market. At first sight this may seem remarkable because the company holds a legal monopoly on a market which is far from being saturated. The management has to strain its resources to the utmost to cope with the spontaneous stream of new subscribers and the ever Increasing traffic. But bearing in mind that the telephone service requires high Investments in cable networks, exchanges and apparatus, it is self-evident that a forecast of future developments is urgently needed. To get an Insight into these developments, different methods are being used, i.e.: 1. Inquiries; 2. Econometric methods such as the analysis of time series and the cross section analysis; 3. Marginal Income method; 4. International comparison, which is based on the principle that a study is made of the trend-of the relevant, quantity in the countries where this quantity has developed further than in the home country. Hereafter the techniques mentioned will be illustrated by means of a brief representation of some applications.