Income concept in Turkish income tax system

The most important problem for Income Tax System is determination of taxable income concept which generate the subject and the tax base of income tax. In Today's contemporary World it is possible to find a lot of discussions in different countries about how income concept would be defined in a simpler way, how it would be more fair and appliable. Different country practices shows that there is no any consensus about definition of income concept. In other words, some values which is subject to income tax in some countries may not constitute any value for others. In approximately 50 years period between 1950 (first income tax in a modern way was started to practice) and 1998 (4369 Numbered Law was modified) there was no any important discussion about which values should be a base for income tax. But after this law mentioned above, income concept has been and definition of it one of the most important subjects. In this study, the main income definitions which are accepted as "income" according to Turkish Income Tax System are brought up in a chronacigal order and than offered a comperatif appraisal between this definitions. In this sense, there could be some explanations about definition of "new income" concept which is accepted in new 4369 Numbered Law. When different country practices are also payed attention, new income concept can be evaluated as theorically proper and claimed that it would help to maintaning equity principle of taxing. Neverthless, it should be suggested in order to negative economic conditions, infrastructural and some tecnical insufficiencies, this new income concept should be postponed as parallel to public's general expectations.