Approaches based upon Material Flow Analysis (MFA) and Environmentally Extended Input Output Analysis (EE-IOA) are widely used for studies investigating the environmental impacts which can be attributed to different activities or which might result from proposed activities. This study compares the two approaches with the objective of understanding their relative merits and the conditions for which each approach is appropriate. The approaches often provide contrasting results. This can be due to differing datasets and assumptions but may also reflect underlying differences in what the results represent. In particular the applicability, implications and the boundaries to which the results relate. If the nature of these differences is not appreciated, they can be problematic for the appropriate use of the results. Several hybrid techniques have been developed in order to address these differences and take advantage of the benefits offered by each approach. These clearly have merit. However, it is proposed that where the nature of the differences is appreciated, the different results can complement each other and provide a more expansive understanding of the impacts being investigated. This can be advantageous when the results are used to inform policy decisions or to report progress towards particular goals. To explore this further, a case study relating to the UK steel sector is presented, illustrating the range of results which may be indicated by each approach. In each case, the limitations of each approach and the areas of investigation which may be better addressed by each approach are considered. Analysis of these observations is then combined with a review of previous studies in order to make recommendations. These are presented as a framework highlighting differences and making suggestions for the ways in which each approach can be applied and used to provide complementary insights.