We show that every frame can be essentially embedded in a Boolean frame, and that this embedding is the maximal essential extension of the frame in the sense that it factors uniquely through any other essential extension. This extension can be realized as the embedding L→N(L)→BN(L)\documentclass[12pt]{minimal}
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\begin{document}$$L \rightarrow \mathcal {N}(L) \rightarrow \mathcal {B}\mathcal {N}(L)$$\end{document}, where L→N(L)\documentclass[12pt]{minimal}
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\begin{document}$$L \rightarrow \mathcal {N}(L)$$\end{document} is the familiar embedding of L into its congruence frame N(L)\documentclass[12pt]{minimal}
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\begin{document}$$\mathcal {N}(L)$$\end{document}, and N(L)→BN(L)\documentclass[12pt]{minimal}
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\begin{document}$$\mathcal {N}(L) \rightarrow \mathcal {B}\mathcal {N}(L)$$\end{document} is the Booleanization of N(L)\documentclass[12pt]{minimal}
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\begin{document}$$\mathcal {N}(L)$$\end{document}. Finally, we show that for subfit frames the extension can also be realized as the embedding L→Sc(L)\documentclass[12pt]{minimal}
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\begin{document}$$L \rightarrow {{\mathrm{S}}}_\mathfrak {c}(L)$$\end{document} of L into its complete Boolean algebra Sc(L)\documentclass[12pt]{minimal}
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\begin{document}$${{\mathrm{S}}}_\mathfrak {c}(L)$$\end{document} of sublocales which are joins of closed sublocales.
