Proliferation of WMDs is a grave threat to mankind, be it their flow to ‘irresponsible states’ or to terrorists. Charged by its perception of vulnerability, the US has initiated the Proliferation Security Initiative; seeking involvement of ‘key’ states for interdiction of ‘suspect ships’ at sea. In its present form, PSI is contrary to the principle of ‘Freedom of the Seas’. Further, its operational efficacy is doubtful and it has an escalatory potential. However, bilateral arrangements as an extension of PSI may lawfully supplement global non-proliferation efforts. A ‘larger’ comprehensive solution lies in greater UN involvement and segregation of the threats.