We give a survey of the postulates which provide the framework of quantum field theory. Particular attention is given to the lesser known ones, namely, completeness requirements and ``primitive causality.'' Three field theoretical models are analyzed. These examples show that ``primitive causality'' is not a consequence of the commonly used postulates (which include the ``causal commutation relations''). ``Asymptotic completeness'' is not assured by any of the other postulates listed. In the formulation and analysis the concept of operator rings associated with space-time regions is used extensively.