The LaTeX command for bigcup (⋃) is \bigcup (big union).
\bigcupWriting a paper? The table generator and the BibTeX cleaner are one click away, no account.
Write \bigcup inside math mode, that is between $…$ for inline math or in a \[ … \] or equation block for display math. It is part of core LaTeX math, so no extra package is required.
Set notation lives in math mode: write $\bigcup$, even in the middle of a sentence. With unicode-math under XeLaTeX or LuaLaTeX, typing ⋃ in a formula gives the same symbol.
$A \bigcup B$Open this example in the live preview: it renders as you type, with no compiler and no signup.
\emptyset\varnothing\mathbb{N}\mathbb{Z}\mathbb{Q}\mathbb{R}\mathbb{C}\mathbb{F}^\complement\bigcap\bigsqcup\uplus\biguplus\mathcal{P}Set symbols in LaTeX: the full table or search all 350+ LaTeX symbols.
Use \bigcup in math mode; it needs no extra package. For example, $A \bigcup B$.
None: \bigcup is built into LaTeX, so no extra package is required.