Starting with its 20th anniversary in 1991, every five years brings another double Alligator collection, and 2011 was no exception. While the 35th edition --released in 2006 -- logically featured 35 songs, the compilers couldn't quite squeeze 40 onto this 40th anniversary disc, even though owner Bruce Iglauer does admit to fading a few endings off prematurely in order to maximize the list, which hits 38 selections. The trick with these albums is to both pay tribute to the label's storied past while including enough recent acts to connect the dots between the house-rocking music Iglauer built his company on, and the more modern yet still roots-based sounds he's released during the last five years. He does an excellent job here, mixing not just old and new, but male and female musicians who have recorded for Alligator over the decades. Of course, no Alligator historical collection is going to exclude Hound Dog Taylor, Iglauer's first signing who remains the raucous, soulful blues-rocking standard who helped forge the label's musical direction. Newer artists such as JJ Grey & Mofro, Eric Lindell, Anders Osborne, and Janiva Magness share space with Johnny Winter, Son Seals, Koko Taylor, Albert Collins, Lonnie Brooks, Eddy "The Chief" Clearwater, and lots more. A 30-page book includes obscure information and anecdotes about each, providing a first-hand look at what attracted Iglauer to the artists. Even with 35 acts, dozens are left out, and they are listed individually at the end of the extensive and often fascinating notes. There are some predominantly acoustic performances from Mavis Staples, Saffire -- The Uppity Blues Women, Buddy Guy & Junior Wells, and Corey Harris, but the majority of the selections run to the high-energy, very plugged-in Chicago and Texas blues that Iglauer plainly loves. Between musicians such as Luther Allison, Roy Buchanan, Son Seals, and Koko Taylor, all of whom have created arguably their finest work while signed to Alligator (and that's saying plenty), there is an embarrassment of riches to choose from. While some of these names have also appeared on previous anniversary editions, no songs are repeated from those albums. Clearly, the intention of this and the previous sets is as loss leaders to sell more individual Alligator discs, but they play as perfectly enjoyable mash-ups of roots music, and a historical music lesson that anyone with an affinity for the genre will appreciate.