ROOT is an object-oriented program and library developed by CERN. It was originally designed for particle physics data analysis and contains several features specific to the field, but it is also used in other applications such as astronomy and data mining. The latest minor release is 6.28, as of 2023-02-03. Description CERN maintained a program library written in FORTRAN for many years; development and maintenance were discontinued in 2003 in favour of ROOT, which itself is written in C++. ROOT development was initiated by René Brun and Fons Rademakers in 1994. Some parts are published under the LGPL, and others are based on GPL software and are thus also published under the terms of the GPL. It provides platform independent access to a computer's graphics subsystem and operating system using abstract layers. Parts of the abstract platform are: a graphical user interface and a GUI builder, container classes, reflection, a C++ script and command line interpreter (CINT in version 5, cling in version 6), object serialization and persistence. The packages provided by ROOT include those for Histogramming and graphing to view and analyze distributions and functions, curve fitting (regression analysis) and minimization of functionals, statistics tools used for data analysis, matrix algebra, four-vector computations, as used in high energy physics, standard mathematical functions, multivariate data analysis, e.g. using neural networks, image manipulation, used, for instance, to analyze astronomical pictures, access to distributed data (in the context of the Grid), distributed computing, to parallelize data analyses, persistence and serialization of objects, which can cope with changes in class definitions of persistent data, access to databases, 3D visualizations (geometry), creating files in various graphics formats, like PDF, PostScript, PNG, SVG, LaTeX, etc. interfacing Python code in both directions, interfacing Monte Carlo event generators. A key feature of ROOT is a data container called tree, with its substructures branches and leaves. A tree can be seen as a sliding window to the raw data, as stored in a file. Data from the next entry in the file can be retrieved by advancing the index in the tree. This avoids memory allocation problems associated with object creation, and allows the tree to act as a lightweight container while handling buffering invisibly. ROOT is designed for high computing efficiency, as it is required to process data from the Large Hadron Collider's experiments estimated at several petabytes per year. ROOT is mainly used in data analysis