A large part of the literature on part-time employment stresses that this form of employment contract is the result of employers’ strategies and female employees who need to reconcile work and family life. However, the growth in the number of employees sharing employment and other paid or unpaid interests expands the range and significance of working-time issues. This dissertation claims that where regulation and implementation of working-time transitions are favourable to part-time employment, part-time is likely to expand to more diverse categories of workers than those for whom it was originally intended ( i.e. mothers with caring responsibilities). The research follows a case-oriented comparative approach that draws on documentary information and a total of 48 in-depth interviews with actors’ representatives at three levels: national, sector (education and local government) and organizational, in the UK, the Netherlands and Spain. Initiated in different moments in time, the regulation of working-time transitions appears to follow a similar staged path in the three countries, although the wider institutional context affecting part-time and the active support of main actors varies for each country, especially at the organizational level. In the Dutch case, part-time regulation started off as a mechanism to enable the employment of women with caring responsibilities and, from there, it evolved towards a wider understanding of workingtime flexibility, extending the right to work part-time to other categories of employees. Given the pioneering role of the Netherlands in this area, it could be argued that both the UK and Spain have been following the Dutch example although with different degrees of success. In the Netherlands, after two decades of active support to part-time, there is still a big gender gap among part-timers, and in many sectors and occupations employees face difficulties to change their working hours; still, the general trend seems to be that access to part-time is becoming easier at more sector and occupational levels, in a context where organizations, already facing short full-time working weeks and high percentages of part-time, have been learning to decouple business hours from the different duration of the employees’ shifts. The need to design clear-cut coordination mechanisms that guarantee the steadiness of the service and the 'standardisation' of handing-over procedures, have helped to accept a variety of working-time arrangements. This capacity to dissociate organisations’ operative time from employees’ working hours is also present in British and Spanish 24-hour services, what has favoured exceptional good part-time jobs. However, the political efforts to promote part-time in Spain and the UK are confronted with serious obstacles, their segmented labour forces among them. The long-hours culture in both Spain and the UK, together with the high proportion of temporary contracts in the Spanish case, are the most visible signs of the structural difficulties these two countries face to achieve working-time flexi-curity. In the three countries, there are no clear links between long hours and productivity levels, and the processess that lead to more transparent assessments of work performance seem to facilitate working-time flexibility beyond standard full-time employment contracts. Certainly, different commitments and compromises need to be achieved between conflicting demands and interests about how employees use their own time, but this thesis argues that part-time may help to soften the conflicts between the specialization and hierarchy requirements of the social division of labour and individuals’ time-use autonomy.