If Poison The Well's The Opposite of December marked the end of metalcore's first wave at the tail end of 1999, then Killswitch Engage's self-titled debut officially ushered in the second wave just months later. Killswitch would eventually sign a major label deal with Roadrunner and go on to be one of the biggest metalcore bands of all time, but none of it would have happened without this pivotal debut (released on the now-defunct, then-iconic metalcore/post-hardcore label Ferret). "Before any big labels, world tours, and even the term 'metalcore,' it was just us four guys playing metal steeped in hardcore roots," frontman Jesse Leach said when the album got a 20th anniversary vinyl reissue last year. "We had no regard for a career, ambition, or any thought of longevity or legacy." That very much comes through in the music, which is noticeably rawer and less commercial sounding than what Killswitch would release at the height of their fame, but which was still more crisp and melodic than most '90s metalcore and ended up kicking down the doors for this band and the genre in general. Killswitch helped introduce the influence of Swedish melo-death bands like At The Gates and In Flames into American metalcore; a few years later, there'd be dozens of bands doing the same thing, but the melodic riffage on this LP is some of the first. Guitarist Adam Dutkiewicz's production also helped define the sound of the next decade of metalcore. He'd go on to produce countless definitive metalcore albums -- several of which are on this list -- and he honed his skills making his own band's debut.

Pick up the 20th anniversary edition of Killswitch Engage's self-titled debut on green splatter vinyl in our shop.

Before Eighteen Visions went on to embrace radio-friendly melodic metalcore, and before guitarist/backing vocalist Brandan Schieppati achieved fame fronting his own band Bleeding Through, 18v were following in the footsteps of '90s bands like Converge, Cave In, Coalesce, and Botch. For their sophomore album and Trustkill debut, Until The Ink Runs Out, they took that sound, made it their own, and influenced a ton of other bands in the process. Instead of veering towards atmosphere and art rock like their predecessors did, 18v were all about the brutality. Breakdowns became a cliché by the late 2000s, but Until The Ink Runs Out employed a breakdown-after-breakdown-after-breakdown approach that felt revolutionary (and not cheesy) at the time, while also managing to contain songs that were tuneful but not poppy or glossy. The album ended up forming a bridge between the more hardcore-leaning '90s bands and the machine-gun-chugging 2000s bands, and it remains a record that hardcore kids and Ozzfest attendees can agree on today.

Pick up a vinyl copy of Until The Ink Runs Out in our shop.

The Dillinger Escape Plan helped invent the utterly chaotic subgenre of mathcore with their 1999 debut LP Calculating Infinity, after which Dimitri Minakakis left the band, leaving them without a vocalist. While they searched for a permanent replacement, they recorded the Irony Is a Dead Scene EP, and vocals on that were handled by none other than Faith No More/Mr. Bungle's Mike Patton, who was understandably attracted to the totally batshit music Dillinger were making. Once they officially recruited new vocalist Greg Puciato, they released their second full-length Miss Machine (on Relapse), and this time around they were even more batshit. I don't even like calling this album "mathcore"; it's too niche, it undersells it. It's like, I don't know, progressive circus acid freakout avant-goth metallic rock -- definitely a little more Bungle-y than before they worked with Mike Patton -- but still somehow very much a metalcore record. As great as Dimitri Minakakis was, Greg Puciato was perfect for this new sound. His scream is as ferocious as you want from metalcore, but the range of his clean-singing voice matched the growing musical range of the band's instrumentalists. Like on their debut, band members Ben Weinman and Chris Pennie co-produced the album with pioneering metalcore producer Steve Evetts (Deadguy, Snapcase, etc), but this time they embraced a warmer, more spacious production style that really gave these ambitious songs room to breathe. It's obviously weird music, but it's not difficult to listen to. Mixed in with all the looniness is a big, bold rock record with hooks that rivaled anyone in melodic metalcore. Miss Machine did it all, and it never went overboard.

Pick up 'Miss Machine,' 'Calculating Infinity,' and DEP's 2007 album 'Ire Works' on various splatter vinyl variants in our shop.

The Acacia Strain often got lumped in with deathcore, but they really predated that genre's Myspace-fueled boom (with albums dating back to the early 2000s including a trio of Adam D-produced records), though it's not totally impossible to see why. There's definitely some death metal in Vincent Bennett's growl, and the band frequently relies on slam-friendly breakdowns. More so than any other band on this list, The Acacia Strain often seem like their sole purpose is to make the earth shake when they perform. That said, it does a disservice to The Acacia Strain's creativity to only talk about them in terms of pure brutality. They're masters at subtly weaving an atmospheric side into their music, and the way they approach breakdowns always feels artistic. I know "ignorant" is a compliment when talking about breakdowns, but The Acacia Strain's breakdowns feel the opposite of that. It's not easy to pick one album that best represents them -- and if you're looking for TAS at their most strictly metalcore, you're probably better off with 3750 or The Dead Walk -- but 2010's Wormwood found them fusing together metalcore, death metal, post-sludge metal, and Meshuggah rhythms in a way that felt more seamless and more innovative than anything they'd done previously. It's frequently and deservedly considered an even better record than their earliest material, and it put them on the increasingly creative path that they're still on today -- 2019's It Comes In Waves and 2020's Slow Decay may actually be their most unique albums yet. They've also become elder statesmen of the genre, and -- through the guest appearances on Slow Decay, their choice of tourmates, and the local openers that Vincent hypes -- extremely vocal champions of today's hardcore scene. It's important for veteran bands to keep their ear to the ground the way Vincent has, and it's no surprise that many of today's best bands are eager to tour and collaborate with them. The Acacia Strain helped pave the way for so many of them.

Pick up Wormwood on limited orange/yellow vinyl in our shop.