This chapter introduces the SSLD (Strategies and Skills Learning and Development) System as a comprehensive model for practice in psychosocial service for seniors. The challenges and issues associated with aging are complex, and involve physical, biological, psychological, social, existential and spiritual dimensions. In order to address them in a comprehensive and balanced manner, we need to draw on an extensive set of knowledge, experience and skills taken from various healthcare and human service professions. The SSLD system is built on a meta-theoretical structure that interfaces well with both analytic and holistic conceptualizations of the human person within his or her life-world, or being-in-the-world. Principles and methods of SSLD practice are described through phases of intervention: engagement and problem translation, N3C assessment, 6D (domains of being-in-the-world) formulation, implementation, review and evaluation. These are illustrated with practice examples. Issues related to practice research and knowledge production are also explored.