PYTHIA 6.1 is a high-energy physics event generator that combines PYTHIA 5, JETSET 7, and SPYTHIA. It simulates particle interactions to generate events with high accuracy, incorporating both analytical results and models. The program is designed for use in high-energy physics, including processes like hard scattering, leptoproduction, and hadronic interactions. It supports a wide range of physics scenarios, including supersymmetric physics, beyond-the-standard-model processes, and QCD interactions. The program is written in Fortran 77 and is compatible with Fortran 90. It is tested on various systems, including Red Hat Linux 6.2, and requires about 800 kwords of memory. The program includes features such as parton showers, hadronization, and beam remnants. It has been updated to include new physics processes, improved parton distributions, and enhanced photon physics. The program also includes a detailed description of supersymmetry, strong dynamics in electroweak symmetry breaking, and other advanced physics topics. The program is used to simulate events for experimental comparisons and to study future experiments. It is designed to handle a variety of processes, including those involving supersymmetric particles, technicolor, and other beyond-the-standard-model scenarios. The program includes a comprehensive set of physics processes, with a focus on accurate simulation of event properties. It is intended to generate events that are directly comparable with experimental data. The program has been updated to include new features, such as improved simulations of supersymmetric physics, new processes in beyond-the-standard-model physics, and enhanced descriptions of QCD processes. The program also includes improvements in parton shower matching, hadronization, and decay processes. The program is designed to handle a wide range of physics scenarios, including those involving heavy-flavour production, gauge boson scattering, and Higgs physics. The program is intended to provide a detailed and accurate simulation of high-energy particle interactions.PYTHIA 6.1 is a high-energy physics event generator that combines PYTHIA 5, JETSET 7, and SPYTHIA. It simulates particle interactions to generate events with high accuracy, incorporating both analytical results and models. The program is designed for use in high-energy physics, including processes like hard scattering, leptoproduction, and hadronic interactions. It supports a wide range of physics scenarios, including supersymmetric physics, beyond-the-standard-model processes, and QCD interactions. The program is written in Fortran 77 and is compatible with Fortran 90. It is tested on various systems, including Red Hat Linux 6.2, and requires about 800 kwords of memory. The program includes features such as parton showers, hadronization, and beam remnants. It has been updated to include new physics processes, improved parton distributions, and enhanced photon physics. The program also includes a detailed description of supersymmetry, strong dynamics in electroweak symmetry breaking, and other advanced physics topics. The program is used to simulate events for experimental comparisons and to study future experiments. It is designed to handle a variety of processes, including those involving supersymmetric particles, technicolor, and other beyond-the-standard-model scenarios. The program includes a comprehensive set of physics processes, with a focus on accurate simulation of event properties. It is intended to generate events that are directly comparable with experimental data. The program has been updated to include new features, such as improved simulations of supersymmetric physics, new processes in beyond-the-standard-model physics, and enhanced descriptions of QCD processes. The program also includes improvements in parton shower matching, hadronization, and decay processes. The program is designed to handle a wide range of physics scenarios, including those involving heavy-flavour production, gauge boson scattering, and Higgs physics. The program is intended to provide a detailed and accurate simulation of high-energy particle interactions.