The goal of this thesis was to design a programmable Address Lookup unit for use in the forwarding engine in a network device such as a switch or a router. A solution with a special designed processor core with a optimized Instruction Set, an I/O processor for accesses to external memory and a sample of a network software was designed and mapped to a multiprocessor architecture. The multiprocessor architecture implements the same features as in the current non programmable hardware Address Lookup unit, and adds the possibility to upgrade the implementation to meet new features due to the new property of programmability. Three multiprocessor architectures, the Parallel multithreaded multiprocessor architecture, the Macro pipeline RISC multiprocessor architecture and the Superpipeline VLIW multiprocessor architecture, was selected out as the most suitable implementation architectures. An estimated implementation area for the multiprocessor architectures when meeting the current Address Lookup units performance requirements were calculated. The multiprocessor architectures were compared against each other on the issues of performance and area scalability, where the Superpipeline VLIW multiprocessor architecture was found to be the best implementation platform for the programmable Address Lookup unit. The Superpipeline multiprocessor architecture implementation was built on two basic units, a VLIW processor and an I/O processor. These two basic units was designed, implemented, verified and synthesized. The result of this synthesis was compared with the calculated values made during the target architecture evaluation. For the VLIW processor the estimated implementation area was calculated to 0.141405 mm2 and the final synthesis to 0.156647 mm2, a difference of 11%. The difference was analyzed to depend on the control logic added to the final version of the VLIW processor. For the I/O processor the estimated implementation area was 0.80800 mm2 and the final synthesis 0.106653 2, a difference of 32%. The difference was analyzed to depend on multiplexers added to the final version of the I/O processor. Finally a small Superpipeline, holding eight VLIW processors and two I/O processors, was implemented and synthesized. The implementation area for this synthesis was 0.822874 mm2 compared to 1.466482 mm2 when built and synthesized on separate units. This difference of 78%, was analyzed to depend on the synthesis tools ability to effectively optimize the design.