In response to rising costs and national health system policy change, the Singapore National Healthcare Group reorganized into three Integrated Care Organizations (ICOs), with Yishun Health (YH) responsible for the health of 320,000 residents in Northern Singapore. YH undertook numerous health system transformation (HST) activities in partnership with health and social care providers to improve outcomes.
 HST benefits from greater stakeholder involvement that reinforces agency and encourages exaptive innovations, taking system-wide views that generate prescriptive models for change than descriptive models of problems, and embracing iterative re-design through time. Design thinking (DT), systems thinking (ST), and complexity thinking (CT) offer useful methods and tools with inherent limitations. We applied an integrated DT, ST and CT approach (DSCT) to enable HST within our regional population health system through a series of leadership retreats and envisioning workshops with over 100 teams both within YH and with regional partners, and co-created over 1,000 change ideas to transform YH into a people-centred, value-driven, and integrated regional population health system.
 Health System Transformation Playbook (HSTP) is our DSCT-enabled methodology developed to systematically design, prioritize and test HST actions, anchored on an iterative 3-step process involving story-telling, model building and pathfinding that together tackles the scale of transforming complex adaptive systems through time. HSTP guides that model-building begins with the latest future-state model to ensure new change ideas build on current progress; model boundaries and hierarchy are defined and managed fluidly across scale and time to preserve system coherence; impact analysis of change ideas start at the highest system to optimize primary system purpose, and prescribed interventions with lower agreement or certainty are consciously managed to guard against incremental-only innovations.
 Also resultant is the YH Unified Care Model (UCM) and its cascade of integrated service delivery models based on UCM design principles: 1) biopsychosocial, needs- and assets-based approach to health, throughout a resident’s life course, for the entire regional population, 2) strength- and relationship-based approach to participatory care involving residents, caregivers and community, 3) single care plan across providers, 4) interactions among providers based on population health needs, are strategic, and organizational, 5) care defined from identification to resolution of needs, and system boundaries are defined by the nature of need, 6) coordination of care to efficiently generate health assets while meeting needs, across all sites and transitions of care, 7) carers and care institutions form an ICO and jointly optimize resident-centred outcomes and population value. In turn, the UCM has generated prescribed interventions and prioritized actions to accelerate YH HST including the Integrated Medical Clinic to meet complex chronic medical and social needs, and the UCM Performance Framework. 
 HST is complex and has potential for unintended systemic consequences, and requires local contextualization. HSTP offers a systemic, practice and learning-based HST and organization development methodology that engages people in all health system sub-systems to accelerate change towards people-centred, integrated and value-driven population health systems, demonstrated through UCM. Deeper resident and stakeholder engagement using HSTP and evaluation of HSTP and UCM is ongoing.