परमार्थ मनुष्य का वह नैतिक लक्ष्य जो सर्वोच्च है, जिससे अधिक श्रेयस्कर कुछ हो नहीं सकता, जो मानवीय प्रयत्न का सबसे बड़ा साध्य है। विभिन्न विचारकों ने सुख, आत्म-सिद्धि, शक्ति इत्यादि विभिन्न मूल्यों को सर्वोच्च साध्य माना है। भारतीय दर्शन और परम्परा में इसे निःश्रेयस्, परमार्थ, परम शुभ, परम हित भी कहते हैं। पाश्चात्य परम्परा में "Summum bonum" का सिद्धान्त रोमन दार्शनिक सिसरो (Cicero) ने प्रतिपादित किया था।

Summum bonum is a Latin expression meaning the highest or ultimate good, which was introduced by the Roman philosopher Cicero to denote the fundamental principle on which some system of ethics is based — that is, the aim of actions, which, if consistently pursued, will lead to the best possible life. Since Cicero, the expression has acquired a secondary meaning as the essence or ultimate metaphysical principle of Goodness itself, or what Plato called the Form of the Good. These two meanings do not necessarily coincide. For example, Epicurean and Cyrenaic philosophers claimed that the 'good life' consistently aimed for pleasure, without suggesting that pleasure constituted the meaning or essence of Goodness outside the ethical sphere. In De finibus, Cicero explains and compares the ethical systems of several schools of Greek philosophy, including Stoicism, Epicureanism, Aristotelianism and Platonism, based on how each defines the ethical summum bonum differently.