The Internet Content Adaptation Protocol (ICAP) is a lightweight HTTP-like protocol specified in RFC 3507 which is used to extend transparent proxy servers, thereby freeing up resources and standardizing the way in which new features are implemented. ICAP is generally used to implement virus scanning and content filters in transparent HTTP proxy caches. Content adaptation refers to performing the particular value added service (content manipulation) for the associated client request/response.

ICAP concentrates on leveraging edge-based devices (caching proxies) to help deliver value-added services. At the core of this process is a cache that will proxy all client transactions and will process them through web servers. These ICAP servers are focused on a specific function, for example, ad insertion, virus scanning, multi-AV scanning, content translation, language translation, or content filtering. Off-loading value-added services from web servers to ICAP servers allows those same web servers to be scaled according to raw HTTP throughput versus having to handle these extra tasks.