Four different methods to experimentally determine the J -curve of quasi-brittle materials are analysed and discussed in thiswork. The first twomethods measure the integral of the cohesive law, J (ω), from an initial notch. However, the correct definition of the notch geometry is of critical importance for an accurate identification of the cohesive law. The other two methods measure J (ω) when the crack is propagating with a fully-developed cohesive zone.