In-store digital screens are the fastest-growing surface in retail media — projected to drive 55.9% of all DOOH ad-spend growth between 2025 and 2029. This 2026 operator's guide covers screen technology types, screen-management software vendors, how Walmart, Kroger, Target, Albertsons and Sainsbury's have actually architected their networks, programmatic DOOH (pDOOH) buying mechanics in a post-consolidation market, and the IAB-aligned attribution stack that makes in-store finally measurable.