The Bureau for Paranormal Research and Defense has little to do with Hellboy these days.
The thing with Mike Mignola′s universe is its solidity: a world so convincing and believable that you really could think their stories are at the tip of your fingers, happening in real-time, in the shadows and hidden corners of the world.
With its enhanced meta-humans, such as Abe Sapiens and Liz Sherman; and its human counterparts, like Dr. Kate Corrigan, the team has been a solid back up against the paranormal in all the weird places: deep America, western Europe and northern Russia, to name a few. You enter the stories with a sense of anticipation, and you leave them in a kind of daze, not sure of what reality has in store for you, and that feeling is really the best reason to read comics (or books) in the world, at least for me.
I tend to wait until the omnibus editions get compiled by Dark Horse, since reading one story at a time is just too damn quick. The Trade Paperbacks of all RBPD are available since 2015, and I can′t recommend them enough. Here are the lists and links from the Wikipedia page, if you are interested and don′t have time to browse the page in its entirety:
Plague of frogs. Volume 1 , includes: Hollow Earth & Other Stories; The Soul of Venice & Other Stories and Plague of Frogs. It was released in January 19, 2011 (HC) with this ISBN: 9781595826091. The TPB was released in October 22, 2014 with this ISBN: 9781595826756.
Plague of frogs. Volume 2 , includes: The Dead; War on Frogs and The Black Flame. It was released in August 17, 2011 (HC). The TPB was released in January 21, 2015 with this ISBN: 9781595826763.
Plague of frogs. Volume 3 , includes: The Universal Machine; Garden of Souls and Killing Ground. It was released in March 21, 2012 (HC). The TPB was released in March 25, 2015 with this ISBN: 9781616556228.
Plague of frogs. Volume 4 , includes: The Warning; The Black Goddess and King of Fear. It was released in November 7, 2012 (HC). The TPB was released in May 20, 2015 with this ISBN: 9781616556419.
1946–1948, includes: 1946; 1947 and 1948. It was released in June 10, 2015 (HC) with this ISBN: 9781616556464. The TPB has not come out yet… and I really know what I am getting for Christmas this year.