This thesis presents a thermo-environmental and economic analysis of actual gas-turbine cycle, combined cycle power plants and a proposed trigeneration scheme. The thermodynamic analysis includes the application of energetic and exergetic concepts while environmental analysis embraces the assessment of CO2 emissions in energy production. The economic analysis evaluates the levelized cost of the power plants and financial feasibility of the trigeneration scheme using the basic cost methods. The parametric study is performed to deliberate the effects of various operating and economic parameters on net power output, energy efficiency, exergy efficiency, total heating, total cooling, CO2 emissions and costs. Additionally, regression analysis is performed where various multiple polynomial regression (MPR) model equations have been developed to estimate response variables (performance parameters) as a function of multiple predictor variables (operating parameters). An optimization process has also been performed to present optimal operating conditions for maximum efficiencies with minimum CO2 emissions and levelized costs. The systems have been modeled using Engineering Equation Solver (EES) software and simulated for various conditions. The results of parametric analysis of gas turbine and combined cycle power plants have shown a significant impact of operating parameters on the performance parameters, component exergy destruction, CO2 emission, and costs. The efficiencies and levelized cost of power plants increase with a decrease in the ratio of compressor inlet temperature-to-gas turbine inlet temperature for initial PR values. The effects of pinch point temperature difference and main steam pressure on performance and CO2 emissions are insignificant in the combined cycle power plants. According to the exergy analysis, the combustion chamber and exhaust stack have major contribution towards total exergy destruction/loss rates. Also, the total exergy destruction rate in the regenerative cycle is relatively lower than that in the simple cycle; thereby worked with a higher exergy efficiency. The regression model equations have appeared to be a good estimator of the response variables due to significant R2 values. The optimization results have exhibited an increase in the exergy efficiency and a diminution in the cost rates with the selection of best trade-off values at different power output conditions. The trigeneration system has been investigated parametrically under different modes of operation, i.e., power-heating, power-heating-cooling and power-cooling at different power outputs and varying operating and economic parameters. Two economic indices, i.e., NPV and PBP have been selected with which feasibility of the trigeneration scheme is assessed. Moreover, an evaluation methodology of the trigeneration system has been introduced in a case of heating and cooling of residential buildings in colonies situated near the power plant, taking into account both technical and economic data. The feasibility of trigeneration project for the residential colonies has been assessed after performing heating and cooling demand assessments of the buildings. According to the calculations, hot water consumption per capita is 60 L/d requiring 279 kWh (thermal)/capita per annum, whereas thermal demand for space heating and space cooling are nearly 64 and 109 kWh/m2 floor area, respectively. The trigeneration scheme is determined to be a worthwhile investment for most of the economic conditions and demands. A decrease in the discount rate and an increase in the prices of natural gas and electricity tend to make the trigeneration project more feasible.