Cosmic-ray propagation and interactions in the Galaxy Andrew W. Strong, Igor V. Moskalenko, Vladimir S. Ptuskin Abstract: This paper surveys the theory and experimental tests for cosmic-ray (CR) propagation in the Galaxy up to energies of 10^15 eV. It provides an overview of previous reviews and essential literature, followed by an exposition of basic principles. The paper describes the basic ideas of CR propagation and the physical origin of its processes. It presents the comparison of models with data, including direct and indirect observations, and indicates what can be learned about CR propagation. Some important topics, including electrons and antiparticles, are discussed. The paper discusses the theory of CR propagation, including diffusion, convection, reacceleration, and the structure of the Galaxy. It presents the propagation equation, which describes the transport of CR in the Galaxy. The equation includes terms for diffusion, convection, reacceleration, and energy losses. The paper also discusses the interaction of CR with the interstellar medium, including the production of secondary particles and the effects of magnetic fields and turbulence. The paper discusses the use of various techniques for computing the observational consequences of the theory, including analytical and numerical methods. It presents the comparison of models with data, including direct and indirect observations, and indicates what can be learned about CR propagation. The paper also discusses the importance of CR in understanding the interstellar medium and the role of CR in astrophysics. The paper discusses the use of the GALPROP code for simulating CR propagation in the Galaxy. The code is used to predict the distribution of CR, electrons, positrons, and gamma rays in the Galaxy. The code incorporates current information on Galactic structure and source distributions, and provides a publicly available code as a basis for further expansion. The paper discusses the limitations of analytical approaches to CR propagation and the advantages of numerical methods. It also discusses the importance of self-consistent models in understanding CR propagation and the role of CR in the dynamics of the interstellar medium. The paper concludes with a discussion of the future of CR propagation research and the importance of continued study of CR in the Galaxy.Cosmic-ray propagation and interactions in the Galaxy Andrew W. Strong, Igor V. Moskalenko, Vladimir S. Ptuskin Abstract: This paper surveys the theory and experimental tests for cosmic-ray (CR) propagation in the Galaxy up to energies of 10^15 eV. It provides an overview of previous reviews and essential literature, followed by an exposition of basic principles. The paper describes the basic ideas of CR propagation and the physical origin of its processes. It presents the comparison of models with data, including direct and indirect observations, and indicates what can be learned about CR propagation. Some important topics, including electrons and antiparticles, are discussed. The paper discusses the theory of CR propagation, including diffusion, convection, reacceleration, and the structure of the Galaxy. It presents the propagation equation, which describes the transport of CR in the Galaxy. The equation includes terms for diffusion, convection, reacceleration, and energy losses. The paper also discusses the interaction of CR with the interstellar medium, including the production of secondary particles and the effects of magnetic fields and turbulence. The paper discusses the use of various techniques for computing the observational consequences of the theory, including analytical and numerical methods. It presents the comparison of models with data, including direct and indirect observations, and indicates what can be learned about CR propagation. The paper also discusses the importance of CR in understanding the interstellar medium and the role of CR in astrophysics. The paper discusses the use of the GALPROP code for simulating CR propagation in the Galaxy. The code is used to predict the distribution of CR, electrons, positrons, and gamma rays in the Galaxy. The code incorporates current information on Galactic structure and source distributions, and provides a publicly available code as a basis for further expansion. The paper discusses the limitations of analytical approaches to CR propagation and the advantages of numerical methods. It also discusses the importance of self-consistent models in understanding CR propagation and the role of CR in the dynamics of the interstellar medium. The paper concludes with a discussion of the future of CR propagation research and the importance of continued study of CR in the Galaxy.