To multiclass or not to multiclass? That is very good question, and not an easy one to answer.
Multiclassing, or advancing in more than one character class, has been implemented in many different ways over the long history of Dungeons & Dragons, as well as in other RPGs derived from it. Multiclassing is a way to expand your character's abilities, but there is always a price or drawback to doing so, usually involving slowing (or even halting) advancement in your other class(es).
Multiclassing in D&D
In 1st and 2nd Edition AD&D, you had to choose whether to multiclass when you first created your character. Only certain combinations of classes were allowed (determined by your race), and except for elf fighter/magic-user/thieves, you were limited to two classes. The costs of multi-classing were that your XP were divided between your classes, and your hit points were averaged between your classes. Typically, a multiclass character lagged behind their single-classed companions by a level or two (or more, if triple-classed), and had fewer Hit Dice and HP as a result. Also, in those editions, some classes cost more XP to advance in, so multi-classed magic-users lagged behind even more than usual.
In 3rd Edition D&D, the choice to multiclass was made when you advanced to a new level. Each level you advanced was one level in one class, so your levels in all classes added up to your overall character level. You had to keep your classes within one level of each other or take a penalty to XP, but you ignored that limit for your "favored class" (which was determined by race, or was your first class for humans). This method was well integrated with the introduction of feats and skill ranks based on level, and allowed for the introduction of prestige classes. These special classes were slightly more powerful than a base class, but required characters to meet certain prerequisites before entering them (which could not be met before 6th level at minimum, and sometimes much higher). They otherwise used the multiclassing rules, and ignored favored class limitations.
Multiclassing in 3E (and the later v.3.5 revised rules) allowed for a more customized approach to character concepts. Some adventurers would split their levels fairly evenly between their two (or more) paths. Others might only take a level or two in another class (informally called "dipping a class") to pick up an entry-level ability, such as new armor and weapon proficiencies, or a few useful low-level spells. But every level in one class slowed progression in all others you took, which delayed access to higher-level abilities. Casters in particular sacrificed a significant amount of power by slowing down their spell progression. To offset this, a few prestige classes were designed to allow spellcasters to progress in caster level, but not their other level-based class features. And one prestige class, the mystic theurge, attempted to make advancing in two spellcasting classes a more viable option, with mixed results.
(I did not play much 4th Edition D&D, so don't recall how multiclassing worked in that version of the game, or even if it was an option at all.)
In 5th Edition D&D, multiclassing became an optional rule. This iteration of the game keeps the idea of character level equaling the total of your class levels, but adds prerequisites of minimum scores in the new class's key ability score(s), and has some special rules for acquiring spell slots that are shared between spellcasting classes. Prestige classes were removed from the game, though a few survive (in theme, at least) as subclasses.
Multiclassing in Other d20 Games
Most of my gaming experience these days is with Pathfinder and Starfinder, so with one exception, I'll be focusing on them for the rest of this column.
D20 Modern, which was based on the v.3.0 rules, made multiclassing central to every character's career. All characters started in one of six base classes (one focused on each ability score) for their first few levels, then chose an advanced class to distinguish themselves from other characters. I played very little d20 Modern (and only ever as a GM), but the core assumption that every character would multiclass was rather unique and memorable.
Pathfinder First Edition was a direct offshoot of D&D v.3.5, so its rules for multiclassing and prestige classes were almost identical to that game. The primary change was removing the XP penalty for uneven levels. Instead, your favored class (now always your first class) gave 1 bonus HP or skill rank at each level, which gave a new incentive for staying single-classed. Some classes were adjusted to avoid "front-loading" their class features, making it harder to cherry-pick signature abilities by "dipping." All classes were given powerful capstone abilities at their highest levels, which could only be acquired by single-classed characters. (Pathfinder characters were strictly limited to 20th level.) Finally, some class options and feats could grant a few of the low-level abilities of another class (such as a few minor spell-like abilities, a bonus combat feat, etc.), which could help avoid the need to multiclass.
Starfinder was derived from Pathfinder 1E, but introduced many new rules of its own. It, too, allows multi-classing by choosing one class to advance at each level. However, it provides even more incentives to follow a single class. Most notably, spellcasting progression is slower in Starfinder than Pathfinder, so multiclassing is even more of a sacrifice for casters than in Pathfinder. Most other classes will quickly fall behind in effectiveness, too, particularly the operative and solarian, whose damage output scales with their level in the class. If a character does multiclass, it's strongly advised that they wait until after they've reached 3rd level in their first class, because that's when every class gains Weapon Specialization, which adds bonus damage to weapons with which they are proficient.
Starfinder also offers a new alternative to multi-classing: Archetypes replace some class features at specific levels, but give new abilities instead. This may cause the character to lose or delay access to some class features, or it may simply take the place of a class option like a soldier's bonus feat or an operative exploit. For casters, they typically have fewer spells known at their highest spell levels but their access to those levels isn't delayed. Overall, you retain the full benefits of your class level for purposes of level-based effects and access to most higher-level abilities. Archetypes are also not specific to any one class, but some have prerequisites, particularly if they expand upon the uses for a given skill or proficiency, or modify spellcasting. Finally, unless the GM adopts an optional rule, characters are limited to one archetype (or one per class, if multiclassed).
In Pathfinder Second Edition, multiclassing strongly resembles Starfinder's archetype rules, but you only ever advance in level in one class. However, when you get a new class feat, you can choose to spend it on an archetype dedication feat, which gives some minor initial benefit and allows you to spend future feats on that archetype's feats. Multiclass archetypes give you some (but never all) of the abilities of another class. Other archetypes are unique unto themselves, and may focus on a fighting style, altered ways to cast magic, new ways to use one or more specific skills, or some other theme. (Numerous 1E prestige classes have reappeared as archetypes in 2E, but without the multiclass tag.) Much like in Starfinder, archetypes may be taken by members of any class who meet the prerequisites for the dedication feat, but they are more flexible because you can invest as much or as little in the archetype as you want. There are limits to how many archetypes a character can take, because you can't take another dedication feat until you have taken at least two of that archetype's other feats. That usually means that you can't take a second dedication until at least 8th level, or a third before 16th. (A rare few archetypes include some feats that replace skill feats instead of class feats, allowing faster acquisition.)
When Starfinder Second Edition is released (in playtest at this year's GenCon, and in full next year), it will use the same game engine as Pathfinder 2E, making it fully compatible with that system. Presumably this means that multiclassing will follow the same archetype rules.
My Own History with Multiclassing
In pretty much all of the RPGs I've mentioned above, I prefer to remain single-classed in order to get faster access to the higher-level abilities of my character's first class. There have, of course, been some notable exceptions:
D&D 3E: I once played a fighter who multiclassed entirely for story-based reasons. He took a couple levels of ranger when the party started doing a lot of cross-country travel, and later took some levels in psychic warrior because the campaign's overall story arc involved the emergence of psionic powers among the oppressed classes in a tyrannical empire. I eventually regretted taking so many classes, because while he had an amazing Fortitude save from stacking three martial classes, his Will lagged behind too much, even after taking Iron Will.
At the other extreme, a player in one of my 3E campaigns created a cleric of the god of magic, who multiclassed into wizard. She didn't initially intend to aim for mystic theurge, but once she did, she also picked up a level of loremaster because that class was more interesting than a third wizard level would be. Out of all the characters that I've ever played or GMed, she had the most classes, at four (all by 9th level).
Pathfinder 1E: I have built a handful of characters with the intention of qualifying for a prestige class as soon as possible, including a brawler/living monolith and a rogue/shadowdancer, and a diviner who I never played enough to reach harrower levels. Beyond those, I can only think of four characters offhand who have multiclassed:
- A rogue who took a level of cleric out of thanks to his god for granting him enough luck to survive that long. He later retrained that level back to rogue when it became clear that he could serve his god better by being a better rogue.
- A cleric of Calistria, who multiclassed into rogue as soon as he could. He was originally built as part of an all-cleric party, and they needed to diversify their skill set at 2nd level. (One multiclassed into fighter; the rest stayed single-classed clerics.)
- A ranger who dipped fighter to gain heavy armor proficiency and some bonus feats.
- A hunter/rogue whose teamwork feats plus sneak attack made for very effective flanking tactics with her animal companion.
Starfinder 1E: Out of my 14 Starfinder Society characters, only one is multi-classed. Shortly after acquiring a creature companion, my gnome envoy took a level of xenodruid mystic so that he could speak with animals, like his ancestors once did. That made his companion easier to control, and allowed him to use his language-dependent abilities to help it as well as his PC allies.
I have more characters who have taken archetypes:
- An explorer operative who took the Starfinder forerunner archetype. Her specialization and archetype compliment each other nicely (both do interesting things with Culture and Survival skills). I also already had a high-level operative combat monster, so I felt that sacrificing a few exploits to further differentiate this one was perfectly acceptable.
- A phrenic adept whose species communicates primarily via telepathy, but very slowly (using telepathic message). This archetype solved that problem by giving him limited telepathy (on par with other telepathic PC species), and gave some interesting new abilities as well. The character is a mechanic, so suffers less from investing in an archetype than some other classes would.
- A soldier who became a powered armor jockey. (His archetype starts at 6th level, which he only very recently reached, so I am still waiting to see how effective it is.)
- Another soldier who became a Star Knight.
Pathfinder 2E: Out of 9 Pathfinder Society 2E characters, I have 4 with archetypes (only one of them a multiclass archetype):
- A bookish (but still very social) sorcerer who became a linguist.
- An investigator with the ancient elf heritage, which gives a free multiclass dedication at 1st level. (Normally those are 2nd-level feats.) He took rogue, which provided a few more trained skills to fill in gaps in his already diverse knowledge base.
- A fighter who took the mauler archetype, which focuses on big, two-handed weapons.
- A rogue who took the juggler archetype because of her background as a circus performer.
The release of the Remastered rules last year means that I will eventually be rebuilding these characters, but I will most likely keep the archetypes they have. The first two have classes that did not appear in Player Core, but that I expect to see in Player Core 2, which releases later this summer. The only archetypes in Player Core were the multiclass ones for that book's classes, so I also have to wait to see how many other archetypes get Remastered in the new book before I rebuild my linguist and mauler. The juggler archetype is from an Adventure Path, so I don't expect that to ever get the Remastered treatment, but will continue to exist as-is.
Update 9/15/2024: See Let Me Tell You About My Character: Remastered Edition about the changes I've made to my PFS 2E characters since writing the column above. The short version: The linguist and juggler kept their archetypes; the investigator changed from rogue multiclass to archaeologist; the fighter lost her archetype; and my champion gained one.