This chapter based on a series of lecture notes proposes an overview of mathematical concepts commonly used in medical physics and in medical imaging. One goal is to summarize basic and, in principle, well-known tools such as the continuous and discrete Fourier transforms, Shannon's sampling theorem, or the singular value decomposition of a matrix or operator. Tomographic reconstruction is covered in another chapter. Due to differences in vocabulary, notations and context, it is often difficult to grasp the links between inverse problems as different as image reconstruction in emission tomography,18 photoacoustic tomography,25 image registration, 12 or simply data fitting in the analysis of time sequences. The second goal of this chapter is...