Mascheroni's constant can be expressed by the following integrals: \begin{eqnarray*} \gamma &=& - \int_0^1 \log (- \log x) \, dx \\ \gamma &=& - \int_0^\infty e^{-x} \log x \, dx \\ \gamma &=& \int_0^\infty \left( {1 \over e^t - 1} - {1 \over t e^t} \right) \, dt \\ \gamma &=& \int_0^\infty \left( {1 \over t} - {1 \over 1 + t} - {1 \over t e^t} \right) \, dt \\ \end{eqnarray*}