How to build an army for Warhammer 40,000 second edition.

Art
From the cover of Codex Army Lists

Second edition was a step up from Rogue Trader in that it had army lists from the beginning.

Minimum Maximum
1000 3000

Codex Army Lists recommends 1000 to 3000 point games.

There is no upper limit to the size of an army, but 500 points is about the smallest size for a battleworthy force. A 1,500 point battle will usually last an entire evening, while 3,000 points will give you a battle that will take most of a day to fight. The lists have been designed and balanced for armies of around 3,000 points, but they will work with smaller or larger forces too.

If you fight extremely large battles (say more than 6000 points a side) you may wish to introduce additional restrictions on the number of characters and support items, otherwise these will tend to dominate the battle to the exclusion of other troops...

-Rick Priestly & Jervis Johnson with Alan Merrett, Codex Ultramarines

The cheapest Space Marine army that can be chosen from Codex Army Lists is 180pts with the mandatory Space Marine Commander (without wargear) and a Scout Squad.

In White Dwarf 206 the staff settled on 600pts as the minimum for small games as this allows enough overhead to include an Eldar Avatar.

It's a great game when you play it around 750-1000 points. It starts to creak when you get to 1250...

-Andy Chambers, Filmdeg Miniatures interview (2023)

Army Structure

Players choose their armies using a liberal percentage-based system.

Second edition army lists divide miniatures into three or four broad categories. Typically, the categories are characters, squads and support. Occasionally these will have other names. Orks have mobs instead of squads, Tyranids have individuals instead of characters, but they are functionally equivalent. Allies are chosen from the support allocation which also tended to include vehicles and artillery.

Codex Army Lists

Booklet covers
The Rules

Codex Army Lists is a booklet in the core box set.

Army List Characters Squads Support Other Allies
Space Marines 0-50% 25-100% 0-50% Imperial Agents; Imperial Guard; Squats; Eldar
Imperial Guard 0-50% 25-100% 0-50% Auxilia: 0-50% Space Marines; Imperial Agents; Squats; Eldar; Orks
Imperial Agents Allies to Space Marines or Imperial Guard: 0-25%
Squats 0-50% 25-100% 0-50% Space Marines; Imperial Guard; Eldar
Orks 0-50% 25-100% 0-50% Freebooters: 0-50% Chaos; Imperial Guard (requires Blood Axe mob)
Eldar 0-50% 25-100% 0-50% Space Marines; Imperial Guard; Squats
Chaos 0-50% 25-100% 0-50% Daemons: 0-50% Orks
Tyranids 0-50% 25-100%
Genestealers 0-50% 25-100% 0-50% Tyranids or Chaos

This book is also known to fans as The Black Codex.

Codices

Book covers
Codex Covers
Codex (Army) Characters Squads Support Other Allies
Angels of Death (Blood Angels) 0-50% 25-100% 0-50% Any Space Marine lists; Imperial Guard; Imperial Agents; Squats; Eldar
Angels of Death (Dark Angels) 0-50% 25-100% 0-50% Any Space Marine lists; Imperial Guard; Imperial Agents
Assassins Expansion for Imperial Agents
Chaos (Space Marines) 0-50% 25-100% 0-25% Daemons: 0-25% Any Chaos lists; Orks; Genestealer Cult; Imperial Guard
Chaos (Cult) 0-25% 25-100% 0-50% Any Chaos lists; Orks; Genestealer Cult; Imperial Guard
Chaos (Daemon World) 0-50% 25-100% 0-25% Any Chaos lists; Orks; Imperial Guard
Eldar 0-50% 25-100% 0-50% Harlequins: 0-50% or 100% Any Space Marine lists; Imperial Guard; Squats
Imperial Guard 0-50% 25-100% 0-25% Any Space Marine lists; Imperial Agents; Eldar; Squats
Orks 0-50% 25-100% 0-50% Restricted items from Space Marine & Imperial Guard lists
Sisters of Battle 0-50% 25-100% 0-15% Allies: 0-25% Any Space Marine lists; Imperial Guard; Imperial Agents
Space Wolves 0-50% 25-100% 0-50% Any Space Marine lists; Imperial Guard; Imperial Agents; Squats; Eldar (not Avatar)
Tyranids (Tyranids) 0-50% 25-100% 0-50%
Tyranids (Genestealer Cult) 0-50% 25-100% 0-25% Chaos
Ultramarines 0-50% 25-100% 0-50% Any Space Marine lists; Imperial Guard; Imperial Agents; Squats; Eldar (not Avatar)

Others

A few other army lists made it into the White Dwarf and Citadel Journal magazines.

Army Source Notes
Adeptus Arbites WD169 As Imperial Agents with special shotgun ammo
Death Company WD188 Single unit; predated Codex Angels of Death
Legion of the Damned WD195 Expansion of unit in Codex Ultramarines
Space Marines WD209 Expansion for Space Marine lists
Necrons WD217 & WD218 0-50% / 25-100% / 0-50% split; only 4 units to choose from
Legion of the Damned WD225 0-50% / 25-100% / 0-25% split
Rogue Traders CJ9 0-50% / 25-100% / 0-50% split with Imperial Guard & Space Marine allies
Eldar Exodites CJ12 Expansion for Codex Eldar
Penal Legion CJ12 Expansion for Imperial Agents
Pirates CJ13 & CJ14 0-50% / 25-100% / 0-50% split

Example Armies

Most players prefer to collect their armies in blocks of 500 or 1,000 points' worth of troops. For example, you might begin with a core force of 500 points and built it up by adding 500 point blocks at a time. This allows you to conveniently plan your purchases and gives you time to paint the models and try them out on the tabletop before deciding what to add next.

-Rick Priestly & Jervis Johnson with Alan Merrett, Codex Ultramarines
Factions Points Publication Nature
Space Wolves; Orks ~2000 Codex Space Wolves Battle report
Imperial Guard 1500 Codex Imperial Guard Sample army
Orks vs Eldar 1500 White Dwarf 171 Battle report
Space Marines; Imperial Guard; Orks 2000 White Dwarf 182 Battle report
Space Marines; Imperial Guard n/a White Dwarf 187 Battle report
Imperial Guard; Eldar; Tyranids 3000 White Dwarf 189 Battle report
Dark Angels; Orks 1500 White Dwarf 194 Battle report
Eldar 1500? White Dwarf 196 Battle report
Chaos; Orks 1500-2000 White Dwarf 196 Battle report
Orks 1000-2500 White Dwarf 201 Sample army
Eldar; Imperial Guard 1500 White Dwarf 202 Battle report
Tyranids; Space Wolves 1500 White Dwarf 205 Battle report
Blood Angels 500 White Dwarf 209 Sample army
Blood Angels; Eldar 2000 White Dwarf 219 Battle report
Imperial Guard; Orks n/a White Dwarf 222 Battle report
Imperial Guard n/a White Dwarf 222 Unit selection guide
Chaos 1500 White Dwarf 222 Sample army

The battle report in Codex Space Wolves was played using in-development rules so the forces chosen do not match the codex points costs. The WD187 report was a special vehicle battle where points costs were moot. The WD222 report had special rules inspired by the 1964 film Zulu and even featured a farm truck and some civilians.

Some battle reports were restricted to whatever the 'Eavy Metal team had painted - often, no more than one of each unit. This isn't a bad pattern to follow if you want a varied list with a broad range of miniatures and weaponry.

In the WD196 battle report two tournament winners faced off. Each provided detailed reasoning of why they had chosen each unit.

I've got a large unit of Striking Scorpions for no other reason than I like them! (laughs) I just like them, and I've given them all back banners, so they're quite pretty.

-Lawrence Widdicombe, White Dwarf 196

I also like to have a mix of weapons, so that I don't seem to be "power-gaming", so they're not all armed with shuriken catapults.

-Wai Lam, White Dwarf 196

Adie Wood's article in White Dwarf 201 would be my pick for the best monograph on building a 2nd edition army.