The analysis in this book demonstrates the existence of very different screening systems of FDI on national security grounds around the world. They all have different premises and organisational structures, diverse scopes and objectives, and varied forms of implementation. In some jurisdictions, these systems are considered a last resort and recourse to them is only possible when other national legislation of a different nature, for example competition law, is not applicable. The wave of international M&As has led many governments to enact legislation to strengthen aspects of competition policy; this the case, for instance, in Canada. In other places, however, screening systems are applied at the same time as, or with priority over, these other pieces of legislation. These pieces of legislation are granted a national security dimension which they lacked when they were actually enacted.

However, at the same time, these kinds of devices coincide with the generation of similar concerns as regards their impact on FDI, the lack of transparency about how they function, their potential for politicisation and the uncertainty of the response given. The principle of proportionality is essential in fighting this idea of using national security provisions on a protectionist basis, not aiming directly at controlling national security, but instead at adopting hidden economic or strategic goals via a broad reference to national security and related notions.

The imposition of screening requirements does not necessarily have a negative impact on foreign investments flows even when, as has already been mentioned, the system is opaque and susceptible to political influence. However, this is a general principle that needs to be qualified, taking into account the individual characteristics of each specific system, since practice shows that there are many differences between the various existing models. Many countries now reserve the right to block a foreign investment on national security, national essential security interests or related grounds, but it is not always clear what national security means and how, when and in relation to whom this threat is assessed. Moreover, in many cases the evaluation of FDI proposals by state administrations indicates that these administrations have an enormous amount of discretion and that the evaluation procedure is subject to politicisation.