Hello! We are excited to announce the release of Grackle 3.0! The Grackle is a library for chemistry and radiative cooling in astrophysical simulations and models. We are also happy to announce the Grackle method paper, submitted to MNRAS and available on arXiv today as 1610.09591, viewable here: https://arxiv.org/abs/1610.09591. All comments welcome. If you use Grackle in your work, please cite this paper from now on. Grackle 3.0 uses a totally new API that is not backward compatible with Grackle 2.x versions. However, the new API is much more flexible and should allow future development to occur without again breaking backward compatibility. Grackle 3.0 comes with a number of new features: * Support for radiation transfer fields: photo-heating plus HI, HeI, and HeII photo-ionization, and H2 photo-dissociation fields. * Support for field arrays of volumetric and specific heating rates. * Approximate atomic self-shielding of UV backgrounds. * Added Case B recombination cooling rates and updated Case A recombination rates. Minor enhancements: * Updated testing framework. * Documentation improvements. Bugfixes: * Fixed unit normalization for k4 Case B recombination rate. * Fixed scaling of low-density H2 cooling rate and use newer H2 LTE rate in all appropriate places. Grackle can be obtained at: https://bitbucket.org/grackle/grackle The documentation can be found here: http://grackle.readthedocs.io/ Since Grackle 2.0, the Grackle has received contributions from 9 individuals: Greg Bryan Andrew Emerick Simon Glover Nathan Goldbaum Cameron Hummels Edward Leong John Regan Hsi-Yu Schive Britton Smith We thank these people for their contributions. Development of Grackle happens in the open on Bitbucket: https://bitbucket.org/grackle/grackle. We welcome new contributors. -The Grackle development team