YT is an open-source, community-developed toolkit for analyzing and visualizing astrophysical simulation data. It is designed to handle data from multiple simulation codes, including Enzo, Orion, RAMSES, and FLASH. The toolkit provides methods for reading, handling, and visualizing data, including projections, volume rendering, multi-dimensional histograms, halo finding, light cone generation, and topologically-connected isocontour identification. It also includes mechanisms for parallelization of analysis tasks. YT is primarily written in Python with some core routines in C for performance. It utilizes the NumPy library and is a Python module suitable for direct scripting or as a library. It has been used in numerous published papers and posters. YT is designed to be a common platform for simulation analysis, allowing scripts to be shared across groups and analysis to be repeated by independent scientists. The toolkit provides data containers that abstract the underlying simulation data, allowing users to work with physical objects rather than grid patches or files. Data containers can be used to define regions of interest and access data within those regions. YT also provides mechanisms for defining derived fields based on base fields or other derived fields. YT supports multi-dimensional profiles, which are weighted averages or distributions of a variable with respect to other independent variables. It also provides persistent object storage, allowing objects to be saved between sessions and retrieved for further analysis. For visualization, YT provides methods for creating 2D and 3D visualizations of simulation data. It includes slices, projections, cutting planes, and volume rendering. Volume rendering in YT uses direct ray casting and allows for the generation of images describing a simulation. Transfer functions can be defined to control the emission and absorption of light in red, green, blue, and alpha space. YT supports multiple simulation codes, including Enzo, Orion, FLASH, Chombo, and RAMSES. It is designed to work with a variety of simulation codes and has the potential to enable collaboration between different research groups. The toolkit is intended to facilitate cross-group collaboration and validation of results, as well as to lower the barrier to entry for exploratory simulation analysis.YT is an open-source, community-developed toolkit for analyzing and visualizing astrophysical simulation data. It is designed to handle data from multiple simulation codes, including Enzo, Orion, RAMSES, and FLASH. The toolkit provides methods for reading, handling, and visualizing data, including projections, volume rendering, multi-dimensional histograms, halo finding, light cone generation, and topologically-connected isocontour identification. It also includes mechanisms for parallelization of analysis tasks. YT is primarily written in Python with some core routines in C for performance. It utilizes the NumPy library and is a Python module suitable for direct scripting or as a library. It has been used in numerous published papers and posters. YT is designed to be a common platform for simulation analysis, allowing scripts to be shared across groups and analysis to be repeated by independent scientists. The toolkit provides data containers that abstract the underlying simulation data, allowing users to work with physical objects rather than grid patches or files. Data containers can be used to define regions of interest and access data within those regions. YT also provides mechanisms for defining derived fields based on base fields or other derived fields. YT supports multi-dimensional profiles, which are weighted averages or distributions of a variable with respect to other independent variables. It also provides persistent object storage, allowing objects to be saved between sessions and retrieved for further analysis. For visualization, YT provides methods for creating 2D and 3D visualizations of simulation data. It includes slices, projections, cutting planes, and volume rendering. Volume rendering in YT uses direct ray casting and allows for the generation of images describing a simulation. Transfer functions can be defined to control the emission and absorption of light in red, green, blue, and alpha space. YT supports multiple simulation codes, including Enzo, Orion, FLASH, Chombo, and RAMSES. It is designed to work with a variety of simulation codes and has the potential to enable collaboration between different research groups. The toolkit is intended to facilitate cross-group collaboration and validation of results, as well as to lower the barrier to entry for exploratory simulation analysis.