This thesis is a summary of the process of design of the hardware and firmware associated of an electronic tracking tag for marine wildlife. It includes the aspects of analysing the tags already existing and its main features. Then, proposing a design that fulfils the requirements of these devices. Assemble a first prototype, designing the PCB previously and test its functionality using the firmware designed for the tasks it has to perform as a real product. Finally, proposing a second version of the hardware, attempting to provide a final solution that can be used in a next stage of the project of designing a completely functional electronic tag.