Standardization of solver input languages has been a main dr iver for the growth of several areas within knowledge representation and reasoning, fostering the exploitation in actual applications. In this document we present the ASP-Core-2 standard input language for Answer Set Programming, which h as been adopted in ASP Competition events since 2013. KEYWORDS: Answer Set Programming, Standard Language, Knowledge Rep resentation and Reasoning, Standardization 2 Calimeri et al. 1 Introduction The process of standardizing the input languages of solvers for knowledge representation and reasoning research areas has been of utmost importance for the growth o f the related research communities: this has been the case for, e.g., the CNF-DIMACS format for SA T, th en extended to describe input formats for Max-SA T and QBF problems, the OPB format for pseudo-Boolean problems, somehow at the intersection between the CNF-DIMACS format and the LP format for Integer L inear Programming, the XCSP3 format for CP solving, SMT -LIB format for SMT solving, and the STRIP S/ PDDL language for automatic planning. The availability of such common input languages have l ed to the development of e ffi cient solvers in di ff erent KR communities, through a series of solver competitio ns that have pushed the adoption of these standards. The availability of e ffi cient solvers, together with a presence of a common interfac e language, has helped the exploitation of these methodologies in appli cations. The same has happened for Answer Set Programming (ASP) (Brew ka et al. 2011), a well-known approach to knowledge representation and reasoning with root s in the areas of logic programming and nonmonotonic reasoning (Gelfond and Lifschitz 1991), through the development of the ASP-Core language (Calimeri et al. 2011). The first ASP-Core version was a rule-based language whose syntax stems from plain Datalog and Prolog, and was a conservative extension t o the non-ground case of the Core language adopted in the First ASP Competition held in 2002 during the D agstuhl Seminar "Nonmonotonic Reasoning, Answer Set Programming and Constraints"