3族元素指的是元素周期表上第3族（ⅢB族）的金属元素，其元素个数依其周期表的定义而定，元素个数可以为2个、4个或32个，甚至若包括超锕系元素在内，共有68个。（包含第八周期元素₁₂₁Ubu~₁₅₃Upt，以及第九周期的₁₇₁Usu、₁₇₂Usb与₁₇₃Ust（原子序的上限为173））

由于IUPAC未规定周期表有一个指定的格式，因此有几种不同的周期表，同时也影响了3族元素的成员及个数。不论是依哪一种周期表，以下d区的过渡金属均会列在3族元素中：

而其他的元素就会使用周期表的不同，而分为以下的四种：

Group 3 is a group of elements in the periodic table. This group, like other d-block groups, should contain four elements, but it is not agreed what elements belong in the group. Scandium (Sc) and yttrium (Y) are always included, but the other two spaces are usually occupied by lanthanum (La) and actinium (Ac), or by lutetium (Lu) and lawrencium (Lr); less frequently, it is considered the group should be expanded to 32 elements (with all the lanthanides and actinides included) or contracted to contain only scandium and yttrium. The group itself has not acquired a trivial name; however, scandium, yttrium and the lanthanides are sometimes called rare earth metals.