Like this:

\documentclass{article}
\usepackage{multirow}
\begin{document}
\begin{tabular}{cc|cc}
& & \multicolumn{2}{c}{A} \\
\multicolumn{2}{c|}{\&} & true & false \\
\hline
\multirow{2}{*}{B} & true & 1 & 1 \\
& false & 2 & 3
\end{tabular}
\end{document}
or this:

\documentclass{article}
\usepackage{multirow}
\begin{document}
\begin{tabular}{cc|cc}
\multicolumn{2}{c}{} & \multicolumn{2}{c}{A} \\
\multicolumn{2}{c|}{\&} & true & false \\
\hline
\multirow{2}{*}{B} & true & 1 & 1 \\
& false & 2 & 3 \\
\end{tabular}
\end{document}
or this?

\documentclass{article}
\usepackage{multirow}
\begin{document}
\begin{tabular}{|cc|cc|}
\hline
\multicolumn{2}{|c|}{} & \multicolumn{2}{c|}{A} \\
\multicolumn{2}{|c|}{\&}& true & false \\
\hline
\multirow{2}{*}{B} & true & 1 & 1 \\
& false & 2 & 3 \\
\hline
\end{tabular}
\end{document}
or finally (as described in your comment below):

\documentclass{article}
\usepackage{multirow}
\begin{document}
\begin{tabular}{|c|c|cc|}
\hline
\multicolumn{2}{|c|}{} & \multicolumn{2}{c|}{A} \\
\cline{3-4}
\multicolumn{2}{|c|}{\&}& true & false \\
\hline
\multirow{2}{*}{B} & true & 1 & 1 \\
& false & 2 & 3 \\
\hline
\end{tabular}
\end{document}
to my taste, I would choose the first example ...