Cross-references link to sections, figures, tables, and equations using \label and \ref. Place \label{key} after a section heading, caption, or equation, then use \ref{key} or \eqref{key} (for equations) to insert its number.

\section{Introduction}
\label{sec:intro}
 
In Section \ref{sec:intro}, we...
 
\begin{equation}
E = mc^2
\label{eq:einstein}
\end{equation}
 
From equation \eqref{eq:einstein}, we derived...

Compile twice for references to resolve: first pass creates .aux file with labels, second pass reads it and inserts numbers. Always use ~ (tilde) to prevent line breaks: Section~\ref{sec:intro} not Section \ref{sec:intro}.

Citations reference sources in a bibliography. LaTeX uses BibTeX: create a .bib file with bibliography entries, then cite them with \cite{key}:

\documentclass{article}
\usepackage{natbib}
\begin{document}
 
As shown in \cite{einstein1905}, relativity...
 
\bibliographystyle{plain}
\bibliography{references}
\end{document}

The .bib file (references.bib) contains entries:

@article{einstein1905,
  author = {Einstein, Albert},
  title = {On the Electrodynamics of Moving Bodies},
  journal = {Annalen der Physik},
  year = {1905}
}
 
@book{knuth1984,
  author = {Knuth, Donald E.},
  title = {The TeXbook},
  publisher = {Addison-Wesley},
  year = {1984}
}

\bibliographystyle{plain} sets citation format (plain, apalike, natbib, etc.). \bibliography{references} includes the .bib file (omit .bib extension).

To generate the bibliography, compile with: pdflatex main.tex && bibtex main && pdflatex main.tex && pdflatex main.tex. The bibtex command generates the formatted bibliography from the .bib file. Two final pdflatex runs resolve references.

Citation styles: \cite{key} produces a number [1] or author-year depending on the bibliographystyle. \citet{key} (textual) produces “Author (Year)”; \citep{key} (parenthetical) produces “(Author Year)”. Requires natbib package.

URL citations: Use @misc entries for websites:

@misc{wikipedia2024,
  author = {Wikipedia},
  title = {Article Title},
  url = {https://...},
  year = {2024}
}

Hyperref integration: With \usepackage{hyperref}, citations become clickable links to the bibliography.