公共经济学（英语：Public economics）为经济学的一支，过去多以财政学命名，然就近代经济学发展而言，财政学一词已无法涵盖其学说内容，近代也有人称之为公共部门经济学（英语：public sector economics）。公共经济学所探讨的主体，多与政府部门或是公共部门有关，除了讨论政府的租税、公债与支出外，尚包含了政策效果，以及财政分权，国际公共财等。在经济哲学发展上，为了达成个人与人民的最大利益，公共经济学对于政府部门有两种几乎相对的看法，一是视国家为有机体（英语：Organic），政府就好比人的心脏，而个人则担当了人身上某个组织或者是细胞，国家或者社会的意愿优于个人之上，个人的价值来自于在社会的价值；另一为视国家为机器（英语：Mechanistic），政府仅是为达成个人意志的工具，政府应为个人意志所驾驭。然而所谓「个人最大利益」为何？个说纷纭，有极力压缩政府权力，强调个人自由的自由主义（英语：Liberalism），也有强调伸张政府权力，追求个人社会价值最大化的社会民主主义（英语：Social democracy）。

Public economics (or economics of the public sector) is the study of government policy through the lens of economic efficiency and equity. At its most basic level, public economics provides a framework for thinking about whether or not the government should participate in economics markets and to what extent its role should be. In order to do so, microeconomic theory is utilized to assess whether the private market is likely to provide efficient outcomes in the absence of governmental interference. Inherently, this study involves the analysis of government taxation and expenditures. This subject encompasses a host of topics including market failures, externalities, and the creation and implementation of government policy. Public economics builds on the theory of welfare economics and is ultimately used as a tool to improve social welfare.