LOBSTER is a computer program designed to extract chemical bonding information from periodic plane-wave (PAW) density-functional theory (DFT) output, applicable to a wide range of first-principles simulations in solid-state and materials chemistry. The program incorporates analytic projection routines and offers improved functionality, including the calculation of atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the bond-weighted distribution function (BWDF). LOBSTER is available for free non-commercial use. The introduction reviews the historical development of methods for electron partitioning in molecules, such as Mulliken's approach and the Crystal Orbital Overlap Population (COOP) and Crystal Orbital Hamilton Population (COHP) schemes. These methods have been adapted for use with plane-wave (PW) basis sets, which are essential for many condensed-matter quantum-mechanical codes. LOBSTER addresses the challenge of projecting PW functions onto localized orbitals, using an analytical formalism developed by the authors. The methods section details the process of finding suitable local auxiliary basis functions, which are essential for accurate projection. The program includes an improved definition of "absolute spilling" and "absolute charge spilling" to assess the quality of projections, as well as the root-mean-square error (RMSp) method. Löwdin’s symmetric orthonormalization (LSO) is applied to both the projected wavefunctions and the basis functions to ensure proper projection of densities of states (pDOS) and other bond-analytical tools. The visualization feature allows users to examine the causes of imperfect projections by visualizing the projected and PAW wavefunctions on a user-defined grid. Technical aspects of LOBSTER, including its implementation in modern C++, multi-platform support, and parallelization, are also discussed. The article concludes with two representative applications: the analysis of atomic motion in phase-change materials (PCMs) and the orbital origins of ferromagnetism in α-iron and Ru monolayers. These applications demonstrate the versatility and effectiveness of LOBSTER in exploring complex materials and phenomena.LOBSTER is a computer program designed to extract chemical bonding information from periodic plane-wave (PAW) density-functional theory (DFT) output, applicable to a wide range of first-principles simulations in solid-state and materials chemistry. The program incorporates analytic projection routines and offers improved functionality, including the calculation of atom-projected densities of states (pDOS), projected crystal orbital Hamilton population (pCOHP) curves, and the bond-weighted distribution function (BWDF). LOBSTER is available for free non-commercial use. The introduction reviews the historical development of methods for electron partitioning in molecules, such as Mulliken's approach and the Crystal Orbital Overlap Population (COOP) and Crystal Orbital Hamilton Population (COHP) schemes. These methods have been adapted for use with plane-wave (PW) basis sets, which are essential for many condensed-matter quantum-mechanical codes. LOBSTER addresses the challenge of projecting PW functions onto localized orbitals, using an analytical formalism developed by the authors. The methods section details the process of finding suitable local auxiliary basis functions, which are essential for accurate projection. The program includes an improved definition of "absolute spilling" and "absolute charge spilling" to assess the quality of projections, as well as the root-mean-square error (RMSp) method. Löwdin’s symmetric orthonormalization (LSO) is applied to both the projected wavefunctions and the basis functions to ensure proper projection of densities of states (pDOS) and other bond-analytical tools. The visualization feature allows users to examine the causes of imperfect projections by visualizing the projected and PAW wavefunctions on a user-defined grid. Technical aspects of LOBSTER, including its implementation in modern C++, multi-platform support, and parallelization, are also discussed. The article concludes with two representative applications: the analysis of atomic motion in phase-change materials (PCMs) and the orbital origins of ferromagnetism in α-iron and Ru monolayers. These applications demonstrate the versatility and effectiveness of LOBSTER in exploring complex materials and phenomena.