This is a conceptual introduction to astrophysical processes, at the advanced-undergraduate level. Topics are developed in more or less their historical order of discovery, but from a modern perspective. The book begins with orbits, gradually building in complexity to chaos, relativistic orbits and gravitational lensing, and eventually a semi-classical treatment of gravitational-wave sources. The second part is about how stars work, including related topics like the mass—radius relations for planets and stellar remnants. The third part is about the expanding universe and its history, the concluding section being about fluctuations in the microwave background. More than 60 exercises range from small conceptual puzzles to numerical solution of differential equations, for example, to find the value of Chan-drasekhar’s limit. An unusual feature of the book is the adaptive choice of units according to context, and unit con-versions, such as to and from Planckian units, are an important thread in the book. Observed phenomena are generally derived from basic principles and processes, with an emphasis—as highlighted in the title—on physical problem solving and approximation throughout.