Multi hop wireless networks (MHWNs) are evolving rapidly in recent years as they provide an inexpensive way of achieving the goal of ubiquitous communication for a variety of applications. However they pose many challenges for the communication protocols due to their intrinsic characteristics, such as shared wireless medium, multi hop wireless connection, dynamic topology, decentralized control, and autonomous nodes. Thus, enhancing the performance of end-to-end communication services is a challenging task in MHWNs, and should be addressed by all the protocol entities involved. In this context, the thesis aims to address this challenging task from the transport protocol point of view. The thesis first investigates the performance of end-to-end congestion detection mechanisms, and reveals their limitations on detecting network congestion in MHWNs. This investigation clearly demonstrates the necessity of a cross layer approach for improving the effectiveness of congestion control mechanisms in such networks. Consequently, the thesis recommends a systematic cross layer approach for improving the transport layer performance in MHWNs while maintaining the key benefits of the layered architecture. Following this approach, it proposes a link adaptive transport protocol (LATP) for improving the quality of service (QoS) performance of multimedia streaming applications in MHWNs. LATP adaptively controls the traffic load at the transport layer based on the feedback information received from the network, hence avoiding network overloading as well as improving the QoS performance. The thesis also proposes a set of modifications to TCP congestion control mechanism in order to improve the performance of reliable data delivery applications in MHWNs. In this way, the thesis contributes two novel transport protocol solutions for improving the QoS performance of multimedia streaming and reliable data delivery applications in MHWNs. Furthermore, lack of a simplified framework for analytically investigating the performance of communication protocols in MHWNs brings ambiguity in further development. Toward this problem, this thesis proposes a simple, but elegant and accurate analytical framework for modeling the performance of IEEE 802.11 DCF in MHWNs, and thereby establishing a methodology to investigate the optimal traffic load on multi hop traffic paths in various network conditions.