The Forrester report "Mobile Needs A Four-Tier Engagement Platform" outlined the enterprise architecture required for a successful digital strategy that serves customers via web and mobile channels, while positioning for future touchpoints such as smart products and Internet of Things. The aggregation tier is the heart of modern enterprise architecture; it maps incoming requests for data to the underlying services that provide it, filters context, and provides operational awareness that enriches customer engagements. This report takes a closer look at the aggregation tier — the challenges, benefits, implementation options, and priorities for architects and developers transitioning to a four-tier architecture.