In this article, I aim to explore the interpretation and implementation of United Nations (UN) Security Council mandates authorising the protection of civilians (PoC) and, in particular, the meaning of an authorisation to use ‘all necessary means’ to protect civilians. Over the past two decades, the UN Security Council has repeatedly provided UN (mandated) peace operations with an explicit mandate to protect civilians. In doing so, it has typically authorised the use of ‘all necessary means’ to achieve the aforementioned objective. This PoC language has been subject to varying interpretations and implementations in practice and is therefore often considered ambiguous. The conclusion reached in this article is that PoC language is indeed vague, but that this is not necessarily problematic. It might even be unavoidable in light of the cascade structure in which the PoC mandate is placed and whereby the PoC mandate is interpreted and implemented at the various levels of authority, command, and control. What is problematic is that there is uncertainty and discussion about the limits to the use of force in the implementation of PoC mandates. After all, the formula to use ‘all necessary means’ cannot be regarded as a ‘blank cheque’ to use any amount of force. Therefore, I identify the upper limit to what UN (mandated) peace operations may lawfully do to protect civilians when being provided with a mandate to use ‘all necessary means’. I also detect an emerging lower limit for what UN (mandated) peace operations must lawfully do to protect civilians when being provided with such a PoC mandate.