This article presents an analysis of the sustainable development of generation sources in the Polish National Electric Power System (NEPS). First, the criteria for this development were formulated. The paper also discusses the current status of generation sources, operating in power plants and combined heat and power (CHP) plants of NEPS. Furthermore, it includes a prediction of power balance in NEPS, determining; predicted electricity gross use, predicted demand for peak capacity during the winter peak, predicted demand for peak capacity during the summer peak and required new capacity of centrally dispatched generation units (CDGUs) in 2025, 2030, 2035 and 2040 that would ensure NEPS operational security. Twenty prospective technologies of electricity generation and combined electricity and heat production were analyzed. These were divided into three groups: system power plants, high- and medium-capacity combined heat and power (CHP) plants, as well as small-capacity power plants and CHP plants (dispersed sources). The unit costs of electricity generation discounted for 2021 were calculated for the analyzed technologies, taking the costs of CO₂ emission allowances into account. These costs include: capital costs, fuel costs, maintenance costs, operation costs and environmental costs (CO₂ emission allowances). This proceeds to a proposal of a program of the sustainable development of generation sources in NEPS, which includes the desired capacity structure of power plants and CHP plants, and the optimal structure of electricity production in 2030 and 2040. The results of calculations and analyses are presented in tables and figure.