TemplateTagger is a C++ package for jet substructure analysis with Template Overlap Method. The code operates with arbitrary models within fixed-order perturbation theory and arbitrary kinematics. Specialized template generation classes allow the user to implement any model for a decay of a boosted heavy object. In addition to Template Overlap, the code provides ability to calculate other template shape and energy flow observables. We describe in detail the structure of the package, as well as provide examples of its usage. Program summaryProgram title: Template Tagger v.1.0.0Catalogue identifier: AERZ_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERZ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: GNU General Public License, version 3No. of lines in distributed program, including test data, etc.: 112534No. of bytes in distributed program, including test data, etc.: 1812748Distribution format: tar.gzProgramming language: C++.Computer: PC/Mac.Operating system: Linux/Unix/Mac OS X.RAM: 50 MBClassification: 11.External routines: The code uses the PseudoJet library of the FastJet package (http://fastjet.fr/)Nature of problem:Traditional jet reconstruction techniques are inadequate to properly characterize boosted decays of heavy objects. High luminosity and pileup further complicate the matter as extra soft radiation is deposited within the large jet cones, thus both shifting and broadening the kinematic distributions boosted jets.Solution method:Template Overlap Method attempts to characterize the sub-structure of boosted jets by matching them to the underlying parton level decay configuration. Each boosted jet is analyzed with a large number of possible kinematically allowed structures called templates. The score of the best matching template is used to estimate the likelihood that the event is a heavy boosted jet of interest. The method is robust against pileup as the small template sub-cone size and the insensitivity of Template Overlap to energy depositions outside the template sub-cone limit the ability of pileup to affect the analysis.Restrictions:Depends on the problem one wishes to analyze.Running time:1–100 events per second, depending on the number of templates required for the analysis.