A header-only C++ library is provided with support for dates, time zones, ISO weeks, Julian dates, and Islamic dates. 'date' offers extensive date and time functionality for the C++11, C++14 and C++17 standards and was written by Howard Hinnant and released under the MIT license. A slightly modified version has been accepted (along with 'tz.h') as part of C++20. This package regroups all header files from the upstream repository by Howard Hinnant so that other R packages can use them in their C++ code. At present, few of the types have explicit 'Rcpp' wrappers though these may be added as needed.