A vast body of research and theory underscores the importance of parental warmth/affection (hereby ‘warmth’ and ‘warmth/affection’ are used interchangeably) as a distinct relational process that is fundamental to core developmental processes including parent-child attachment, socialization, emotion recognition and responsivity, and empathic development. The increasing focus on parental warmth as a viable transdiagnostic and specific treatment target for Callous-Unemotional (CU) traits highlights the critical need for a reliable and valid tool for measuring this construct within clinical contexts. However, existing assessment methods have limitations in their ecological validity, clinical utility, and the comprehensiveness of their coverage of core warmth subcomponents. In response to this clinical and research need, the observational Warmth/Affection Coding System (WACS) was developed to comprehensively measure parent-to-child warmth/affection. This paper chronicles the conception and development of the WACS, which adopts a hybrid approach of utilizing both microsocial and macro-observational coding methods to capture key verbal and non-verbal subcomponents of warmth that are currently underrepresented or poorly captured by existing assessment tools. Recommendations for implementation and future directions are also discussed.