Population ethics is a branch of moral philosophy that examines the ethical implications of population size and composition. It addresses questions about how to evaluate the well-being of individuals in relation to the overall population, considering factors like quality of life and the impact of new lives being brought into existence. Key issues in population ethics include the Repugnant Conclusion, which suggests that a very large population with low quality of life could be considered better than a smaller population with higher quality of life. Philosophers like Peter Singer and Derek Parfit have contributed significantly to these discussions, exploring how our choices affect future generations.