Introduction The purpose of this article is to examine the explanations behind the decline in union density in so many countries. For the purposes of this essay we will focus mainly on OECD member countries. As well as looking at some countries outside of OECD nations. According to the OECD; “Union density corresponds to the ratio of employees who are union members, divided by the total number of employees.” (OECD, 2014) Union density is also defined as “the percentage of workers who are union members”. (Machin, 2000). Why are we interested in union membership density? The density of union members – “both in absolute terms and in proportion to their potential electoral base among workers – is a question of great interest to industrial relations practitioners and researchers”. (Carley, 2009) Collective bargaining for nurses and teachers is an example of where this representation is very important. Main body “The decline in union density is a characteristic of most, though not all, developed countries over the last quarter century.” (Ebbinghaus, 1999). The OECD average for the decline in union density since 1980 fell from 33% in 1980 to 17% in 2012. (OECD, 2014) While some countries, in particular the Scandinavian ones (Norway, Sweden, Denmark, Finland and Iceland) have maintained a relatively high density (70% in 1980, 68% in 2012), although it has shown some decline, with only Iceland bucking the trend and showing an increase. This compares to other countries, notably New Zealand and Portugal, where membership has fallen by 48% and 36% respectively, according to OECD statistics. The UK and the US have... half the paper... Chinese Unions: Useless or Changing?. London: The Center for Economic Performance Publications Unit .Morishima, 1999. Why will Japan collapse?,. 1st ed. Tokyo: Washingtonpost.Newsweek Interactive, LLC.OECD, 2014. http://www.oecd.org/. [Online] Available at: http://stats.oecd.org/Index.aspx?DataSetCode=UN_DEN[Accessed 9 June 2014].Park, Y. & Lee, M., 1995. 'Economic development, globalization, and practices. 7th ed. London: Routledge.Shin, J. & Wailes, N., 1997. “The Korean Confederation of Trade Unions: Independent Trade Unionism in Newly Industrializing Countries.” Brisbane: Griffith University.Wagner, S.D., 2002. How did the Taft-Hartley Act come about?. [Online]Available at: http://hnn.us/article/1036[Accessed 9 June 2014].Wal Mart, n.d. http://www.ufcw.ca/. [Online]Available at: http://www.ufcw.ca/Theme/UFCW/files/ManagersToolbox.pdf[Accessed 9 June 2014].