Croteam's Serious Sam franchise is full of remakes, ports, prequels, and spin-offs, which can really confuse newcomers and even experienced Serious Sam players. I've been a fan of the series since 2003 and decided to create this guide to clear up the confusion. Please share it with anyone who might need it and inform me if you notice any outdated or incorrect info.

Mainline games + DLC (Some games have early access and full release dates, e.g. "2016/17")

• Serious Sam: The First Encounter (2001) - Sam's first game. Chronologically the 4th.
  
• Serious Sam: The Second Encounter (2002) - Sequel to TFE.
  → TFE and TSE together are referred to as SS1 / SS Classic.
  - You receive both Classics and Revolution together if you buy just 1 of these 3 games.
  
  
• Serious Sam 2 (2005) - Sequel to TSE.
  + Soundtrack DLC (2021) - 31 tracks.
  
  
• Serious Sam HD: The First Encounter (2009) - Remake of TFE.
  
• Serious Sam HD: The Second Encounter (2010) - Remake of TSE.
  + Fusion DLC (2011) - Merges TFE HD into TSE HD for free if you own both games.
  + Serious 8 DLC (2011) - 8 player characters.
  + Legend of the Beast DLC (2012) - 3 story levels set in TFE, based on scrapped maps from early SS1 builds + 3 Versus maps and 1 Survival map.
  → TFE HD and TSE HD together are referred to as SS HD.
  - Some levels are slightly different in SS HD since this engine doesn't support directional gravity, which allowed you to walk on walls and ceilings in certain areas of SS Classic.
  
  
• Serious Sam 3: BFE (2011) - Prequel to TFE, set in 2113 AD before Sam travels to 1378 BC.
  + Bonus Content DLC (2011) - Soundtrack (39 tracks + 1 vocal version), 1 player character, Devastator gun scope, artbook, documentary, promo videos, posters, box art.
  + Jewel of the Nile DLC (2012) - 3 story levels.
  
  
• Serious Sam Classics: Revolution (2014/19) - SS Classic + new Bright Island campaign in 1 updated game. Made by modders (Alligator Pit) with Croteam's support.
  - You receive both Classics and Revolution together if you buy just 1 of these 3 games.
  
• Serious Sam Fusion (2017) - SS HD + SS3 + DLC + VR (no TLH) in 1 updated game.
  - You get SS Fusion for free if you own any of its supported games, but you must buy each game and DLC separately to unlock them here. You don't get your missing games for free.
  - The Devastator scope and some player characters don't work in SS Fusion.
  
  
• Serious Sam 4 (2020) - Prequel to SS3. Originally revealed as Serious Sam 4: Planet Badass.
  + Deluxe Edition DLC (2020) - Soundtrack (19 tracks + 5 alt versions), Tommy Gun skin for the assault rifle, artbook.
  
• Serious Sam: Siberian Mayhem (2022) - Stand-alone SS4 expansion, made by modders (Timelock Studio) with Croteam's support.
  + Soundtrack DLC (2022) - 9 tracks.

VR games

• Serious Sam VR: The Last Hope (2016/17) - VR-exclusive prequel to SS4.
  
• Serious Sam VR: The First Encounter (2016/17) - VR version of TFE HD.
  
• Serious Sam VR: The Second Encounter (2017) - VR version of TSE HD + LotB DLC.
  
• Serious Sam 3 VR: BFE (2017) - VR version of SS3 without DLC.

Chronological order
TLH → SS4¹ → SS3² → TFE³ → TSE⁴ → SS2
1) Siberian Mayhem is "kind of" set between SS4's The Package and From Earth With Love.
2) SS3's JotN DLC is set between The Power of the Underworld and The Lost Temples of Nubia.
3) TSE HD's LotB DLC is set between TFE's Metropolis and Alley of the Sphinxes.
4) Revolution's Bright Island campaign is set between TSE's The Pit and Ziggurat.

Compact summary (Mainline games and story expansions)

• SS: The First Encounter - Classic/Revolution, HD/VR/Fusion.
  
• SS: The Second Encounter - Classic/Revolution, HD/VR/Fusion.
  + Legend of the Beast DLC - For HD/Fusion (already included in TSE VR).
  + Bright Island - New campaign included in SS Classics: Revolution.
  
• SS2
  
• SS3: BFE - Original/VR/Fusion.
  + Jewel of the Nile DLC - For original/Fusion (not available in SS3 VR).
  
• SS VR: The Last Hope - VR only.
  
• SS4
  
• SS: Siberian Mayhem

Croteam's games are quite cheap and often generously discounted.

All the following games are non-canon, and only SS Xbox was made by Croteam.

• Serious Sam (2001) - First-person shooter for Palm OS.
  
• Serious Sam Xbox (2002) - Xbox port of SS1 with altered gameplay and presentation.
  
• Serious Sam: Next Encounter (2004) - FPS for GameCube and PlayStation 2.
  
• Serious Sam Advance (2004) - FPS for Game Boy Advance.
  
• Serious Sam Double D (2011 original / 2013 XXL) - Side-scrolling shooter.
  
• Serious Sam: Kamikaze Attack! (2011) - Side-scrolling auto-runner.
  
• Serious Sam: The Random Encounter (2011) - Role-playing bullet hell.
  
• Serious Sam: The Greek Encounter (2012) - Twin-stick shooter.
  
• Serious Sam's Bogus Detour (2017) - Twin-stick shooter.
  
• I Hate Running Backwards (2018) - Shoot 'em up.
  
• Serious Sam: Tormental (2019/22) - Rogue-lite twin-stick shooter.

Games and DLC

• Sigils of Elohim (2014) - Free puzzle game released before TTP.
  
• The Talos Principle (2014) - Croteam's atmospheric, philosophical first-person puzzle game.
  + Soundtrack DLC (2014) - 30 tracks + 13 alt versions without Elohim's voice.
  + TTP Bonus Content DLC (2014) - Documentary, terminal text booklet, various image files.
  + Prototype DLC (2014) - Over 100 puzzles from early TTP builds + 2 voices for Elohim.
  + Serious DLC (2015) - Serious Sam voice for Elohim + 1 player model.
  + Road to Gehenna DLC (2015) - New campaign with harder puzzles.
  
• The Talos Principle 2 (2023) - Sequel to TTP, set 1000 years later.
  - Croteam's first game that's not running on Serious Engine, but Unreal Engine 5 instead.
  + Artbook DLC (2023)
  + Soundtrack DLC (2023) - 44 tracks.
  + Road to Elysium (2024) - 3 new campaigns with harder puzzles and different styles: Orpheus Ascending, Island of the Blessed, Into the Abyss.
  
• The Talos Principle: Reawakened (2025) - UE5 remake of TTP + RtG DLC.
  Also includes the new In the Beginning campaign and an in-game puzzle editor.
  
• The Talos Principle 3 (TBA) - Planned sequel to TTP2 and end of the trilogy.
  
  
• The Talos Principle VR (2017) - VR version of TTP + RtG DLC.

Chronological order:
In the Beginning → TTP1 + Road to Gehenna → TTP2 → Road to Elysium (OA → IotB → ItA)

Thanks for reading and possibly sharing this guide.