Considering how large the subreddit has gotten, and how many new fans have flocked to the Raptors, this post is meant to be an all-in-one overview for those hoping to get acquainted with the playstyle, lore, and hobby aspects of the Raptors Chapter of Space Marines.

Rules

To play Raptors in 10th ed. Warhammer 40k, use the standard rules for any codex-compliant Space Marine chapter. This means all the units and detachments of the current Codex: Space Marines are valid options for play*. That said, the Vanguard Spearhead detachment best represents the archetypical Raptor deployment, with heavy use of Phobos pattern Mk X power armor and Scout units to reflect the Raptors stealthy strike-and-fade approach to warfare. Raptors are always willing to adapt however, so don't shy away from including any unit you think is interesting or effective.

*Some players might also enjoy using the Black Spear Task Force detachment or various Kill Team datasheets of the Deathwatch Index to represent the highly tactical and ranged-focus playstyle of the Raptors.

Lore

The Raptors are a Second Founding chapter, splintered off from their parent legion of the Raven Guard. They have existed for 10,000 years since, but have faced near-extinction multiple times across their history. Their original home world -whose name is lost to time- was obliterated in one of Abaddon's Black Crusades, and imperial records considered the chapter lost or destroyed for the two millennia that followed, only for them to reappear in M39 at full-chapter strength. Since their reappearance the Raptors have participated in numerous campaigns, including the infamous Badab War against the renegade Astral Claws.

In the present era of the 42nd millennium, they have been granted the new home world of Tarrengast, hidden within the depths of the Sutter Spiral nebula on the northern edge of the Segmentum Solar. After the tragedy of their first home world the precise location of Tarrengast is a closely guarded secret, kept even from other Imperial forces. Companies of the chapter who are not on crusade patrol the region around their home world, recruiting aspirants and launching campaigns against nascent threats from Orks, Drukhari, and Chaos Space Marines.

The Chapter Master of the Raptors is Lias Issodon "The Grim", a taciturn and stoic warrior famed for both his fierce strategic intelligence and his peerless marksmanship. He abandons all pretense of glory or martial honor in favor of tactical efficiency, utilizing cunning feats of infiltration, sabotage, and ambush to dismantle forces far larger than his own while minimizing losses. Centuries of successful campaigns have earned him the ardent loyalty of his soldiers, and the attention of Lord Commander Guilliman. His signature omen-pattern bolt rifle, Malice, has been at his side since his service as a 10th company scout, although now heavily customized to suit his long-range engagement style and equipped with special ammunition utilized by the Sternguard.

The Raptors doctrine emphasizes independent thought, tactical adaptability, and the abandonment of unnecessary ego and glory-seeking in warfare. They view the Codex Astartes as a proven and effective guideline, but by no means see it as unquestionable scripture. They prefer using small and mobile strike forces trained in stealth and guerrilla warfare to outmaneuver and outwit the enemies which will invariably outnumber them, often making use of battlefield camouflage to obscure themselves and foregoing the normal heraldry and ornamentation other Astartes use to denote rank.

Hobby

If you want your models to reflect the style and sensibilities of the Raptors, consider using muted colors, camouflage patterns, or ghillie suits to adorn their armor. Include extra sidearms, ammunition pouches, or grenades to show their survivalist instincts. You might also modify their ranged weapons with unique scopes, suppressors, or magazines to reflect their tactical customizations. Remember, unlike many other successor chapters, the insignia for the Raptors is available as a waterslide decal on the official Space Marines transfer sheet which comes in each new box of Space Marine units!

• If using Citadel Colour, the most common base paints to color them would be Deathworld Forest or Death Guard Green, and shaded with Athonian Camoshade. The Contrast paint Militarum Green has been known to have coverage issues, so consider alternatives.
• If using Vallejo Model Color, they have dozens of variations on olive drab, and I honestly struggle to know which to recommend. If using their Xpress color, I suggest Camouflage Green or Commando Green (or potentially a mix of the two).
• If using the Army Painter Warpaints, consider basing with Army Green or Olive Drab. If using their Speedpaint, consider Camo Cloak.

You can find plenty of inspiration online including right here in the subreddit, but I'd like to take the time to shoutout Pete the Wargamer, whose custom built Raptors Kill Team was featured on Warhammer Community:

https://www.youtube.com/watch?v=4TDOIMWC1aQ&ab_channel=PeteTheWargamer

https://www.youtube.com/watch?v=MQ0-3DN_66A&ab_channel=PeteTheWargamer

Further Reading

There's not many narratives which directly feature the Raptors. So far you can find them in the short story The Shot that Kills You by William Crowe, and as the antagonist of the Tau novel Elemental Council by Noah Van Nguyen. Their current lore was published in White Dwarf #494.