The increasing demand for wireless based services continues to grow with a multiplicity of standards developing. This is driving a need to develop integrated mobile terminals which have multi-mode capabilities, i.e., multiple communication systems which can coexist. The attention of this paper is focused on the coexistence of multiple communication systems via a simple hardware based structure with the algorithms and architectures developed within the framework of multi-mode terminals. The term multi-mode in this paper is limited to a set of standards and to a receiver that is expected to handle different systems with a low hardware complexity. Dedicated hardware is shared and reused by different systems. Existing specifications DAB, DVB-T, HIPERLAN-2 and UMTS are considered as examples in this paper, although the methodology could be applied to other systems. The systems considered can be classified into two categories: multi-carrier systems and single-carrier systems. This paper considers multi-mode terminals from both the algorithm and the architecture viewpoint, reducing receiver complexity by taking advantage of the commonalities among different specifications and receiver requirements. As an example, a joint channel estimation, chip-level frequency domain equalization and parallel interference cancellation structure for WCDMA is presented.