The DTA regime has thus gained in practical importance. More
than 2,000 bilateral tax treaties, connecting about 180 countries, are
in force today. Cooperation within the OECD has intensified, reflecting
this increased importance. The CFA continually engages in technical
elaboration and adaptation of the model. (OECD, 2008). Essentially
all DTTs are based on the model. The OECD MC represents
the general consensus on international taxation; its principles, norms
and rules also effectively constrain the policies that countries can pursue
unilaterally vis-`a-vis foreign tax revenues (Avi-Yonah, 2006). Although
the rules have become more sophisticated and complex over
time, the basic principles and mechanisms of sovereignty preservation that emerged in the 1920s have remained unchanged (Graetz, 2001: 262–
71).