A Practice Note providing an overview of the requirements for different types of plans (other than multiemployer plans and 403(b) plans) available to employers to permit their employees to accumulate retirement benefits or other post-employment income benefits (often referred to as "retirement plans"), with emphasis on qualified retirement plans. It discusses the difference between defined contribution plans and defined benefit plans, the requirements under the Internal Revenue Code (Code) for a plan to be qualified for favorable tax treatment, and the key additional requirements applicable to retirement plans that are employee pension benefit plans subject to the Employee Retirement Income Security Act of 1974 (ERISA).