This volume presents the principles and methods of sprays (path spaces) and Finsler spaces with many applications in the physical and life sciences. Beginning from the classical theory of sprays, the first chapter presents an introduction to modern Finsler differential geometry. The following three chapters can serve as a comprehensive graduate course using the notions of pre-Finsler connections in spray bundles. Topics covered are the calculus of variations and Finsler metric functions, spaces of constant curvature, projective and conformal geometry, two-dimensional Finsler spaces, and Beswald spaces. Chapter 4 deals with the Finslerian view of dissipative mechanics, thermodynamics and information, and geometrical and electron optics. Chapter 5 discusses, from a Finslerian perspective, ecological problems and models, with particular reference to the Great Barrier Reef. Spray connection theory is shown to be indispensable for a logically consistent theory of social interactions. Projective Finsler geometry and Wagner connection theory are used to model time-sequencing changes in growth and development. Some direct applications to fossil measurements in paleontology are also described. For geometers, physicists and theoretical (marine) biologists, the book can also be used as a supplementary graduate text.