This thesis aims to advance the study of linguistic justice as a variable in public policy and contribute to the development of fair and efficient language policy and planning (LPP). Hence, the focus of the present work lies in the role of the state and creates indicators to evaluate language policy and guide a state's choices under the premise that language policy follows the same rules as any other public policy. The thesis presents an indicator to evaluate linguistic justice. To realize such an instrument, first, it addresses questions of theory and methods. In particular, it formulates an operational definition of linguistic justice suitable to be transposed into instruments for measurement. Secondly, it proposes a set of indicators to analyze and compare the strategies of language policies and planning of different jurisdictions. The field of linguistic justice is fairly new and highly interdisciplinary. Therefore, this thesis applies an interdisciplinary approach to answer the research questions, using methods from normative political theory, welfare economics, and public policy analysis. While addressing the theoretical issues around linguistic justice, this thesis employs concepts from the capability approach. Within this study, linguistic justice is conceptualized as the condition that allows the enjoyment of as many language-based capabilities as possible, where language-based capabilities are those beings and doings that necessarily need language to be enjoyed. In order to select the most relevant language-based capabilities to represent the most fundamental public goods and services, this thesis has applied the Constitutional Approach. Derived from the capabilities' tradition, this method of capability selection looks at the constitutions of a sample of countries to identify the most important beings and doings that the people have decided to codify within the document. This approach is used to select a list of fundamental capabilities that absolutely need a common language between the state and its people. The language-based capabilities identified are assigned a statistical indicator,cwhich responds to a series of criteria, such as accessibility of data and simple computations, to make it an effective yet quick index to populate. Each indicator is populated for the different linguistic groups living in a given jurisdiction, including autochthonous and allochthonous minorities - even though the computation is slightly different according to the identity claims specific to the autochthonous minority. The values of the different indicators are finally aggregated through arithmetic mean, resulting in a unique number that represents the Multidimensional Index of Linguistic Justice for a given jurisdiction. The results of different jurisdictions, or the same one over time, are represented visually through a variation of a box plot organized into four clusters according to the value of linguistic justice scored (low, medium-low, medium-high, high). The Multidimensional Index of Linguistic Justice is a tool designed for policymakers, civil servants, and academics. Like any other policy instrument, its main goal is to bring the attention of the political and scientific community to the issue of the management of linguistic diversity by comparing and commenting on the results of different jurisdictions.