This is the first of two books on Computational Physics, based on a course taught by the author for many years at the University of Oslo and University of Michigan. This book covers the introductory material, while the second companion book tackles more advanced topics. The books describe many of the more popular and widely used algorithms for doing science, from linear algebra and eigenvalue problems to differential equations and Monte Carlo methods, with many examples of applications of these methods to scientific problems. They also give insights into structured programming with an in depth discussion of object orientation with examples. The examples are written using programming languages like C++ and fortran2008, which are very widely used in computational physics. Python examples of the same programs will be available via an accompanying website. Furthermore, the author discusses also how to parallelize programs, with an emphasis on supercomputing issues.