Apparatus, methods and systems for supporting Send with Immediate Data messages using Remote Direct Memory Access (RDMA) and the Internet Wide Area RDMA Protocol (iWARP). iWARP logic in an RDMA Network Interface Controller (RNIC) is configured to generate different types of Send with Immediate Data messages, each including a header with a unique RDMA opcode identifying the type of Send with Immediate Data message, and send the message to an RDMA remote peer using iWARP implemented over an Ethernet network. The iWARP logic is further configured to process the Send with Immediate Data messages received from the RDMA remote peer. The Send with Immediate Data messages include a Send with Immediate Data message, a Send with Invalidate and Immediate Data message, a Send with Solicited Event (SE) and Immediate Data message, and a Send with Invalidate and SE and Immediate Data message.