This book analyses the age-profile of investments in human capital, both theoretically and empirically. It identifies the forces driving the employer and self-financed training investments in different skills, by age and length of service, and points to the importance of the costs and returns to training investments, capital constraints, job turnover propensities, imperfect information and the institutional setting in determining the type and timing of training investments made. The econometric analysis performed, using the International Adult Literacy Survey (IALS), provides an insight into the age-profiles of training participation, duration and volume in a number of OCED countries. The findings of this work are used to make recommendations for future policy directions in the area of continuing adult training (or 'lifelong-learning'), both in terms of the policy goals that are set and the choice of means by which these goals are to be achieved. The content of this book will be of interest to policy makers, as well as to academics concerned with the issue of investment in education and training.