Each year, NATO publishes updated figures on its members’ defense expenditures, based on the NATO definition of the term. Data is also provide with respect to key outside entities; estimates are presented for Russia as well. The alliance has been tracking defense spending since 1963, and the figures are available in PDF, HTML, and Excel formats, depending on the year.
As the 2007 publication [PDF] notes:
“The figures given in Table 1 represent payments actually made or to be made during the course of the fiscal year. They are based on the NATO definition of defence expenditures. In view of the differences between this and national definitions, the figures shown may diverge considerably from those which are quoted by national authorities or given in national budgets. For countries providing military assistance, this is included in the expenditures figures. For countries receiving assistance, figures do not include the value of items received. Expenditures for research and development are included in equipment expenditures and pensions paid to retirees in personnel expenditures.”