Creating different congestion control modules (CCMs) that can be plugged into a network communications stack (e.g., a TCP/IP stack). Software abstractions defining transport control events, congestion control algorithms and other information may be exposed by an application programming interface, e.g., of an operating system, and these abstractions may be used to define a CCM. The network communications stack may be configured to select one of multiple available CCMs to control congestion for a given connection. This selection may be based on any of a variety of factors including, but not limited to: network environment; connection path characteristics; connection link characteristics; a value of a socket parameter of an application; other factors; and any suitable combination of the foregoing. Thus, CCMs may be selected and implemented on a per-connection basis.