This report gives the philosophy followed by the CIGRE WORKING GROUP to prepare the Second International Enquiry on high voltage circuit-breaker failures and defects in service. The objectives of the survey are given. The main objective is to compare the results of the Second International Enquiry with those of the First Enquiry. The report also presents the new questionnaire to collect the data on the population of circuit-breakers in service and on each failure observed, together with the definitions and failure classification applicable to the enquiry. Finally, it gives the preliminary results of the Second Enquiry concerning the data of 1988 (first year of the enquiry).