The purpose of this work is to study the usufruct of social actions and participations. It is an institution whose importance can not be minimized, from the point and time that the Spanish legislator (common and regional) makes a wide use of usufruct in family and inheritance institutions. This means that many of these rights are born every day, from the point and time of the well-known phenomenon of the increase in the personal wealth of individuals and families. In fact, it should not be ignored that although at other times wealth was fundamentally real estate or pecuniary, in ours the savings of private individuals are channeled in a decisive way through corporate instruments. In the same way, more and more, even small companies tend to adopt corporate forms, and a very important part of saving (especially in the current situation of low interest rates) is placed in the stock markets, either directly, or through institutions of collective investment that often adopt corporate forms. This proposition immediately refers to a very broad list of legal institutions. On the one hand, we are dealing with real rights, a category traditionally opposed to credit rights. However, the object usufructuado is far from being a corporeal thing, but are the actions and social participations, whose nature has been controversial matter. However, the possibility of incorporating shares in securities determines that the usufruct over tangible things can not be excluded without further ado. At the same time, the shares are susceptible to being represented by book entries (which is now mandatory for their quotation in the stock markets), implying a special regime. Therefore, it seems that the study of the proposed topic should start with a few reflections on the nature of real rights, distinguishing ownership of limited real rights, and, in particular, the phenomenon of usufruct rights, both real and personal. The possibility of usufruct over credit rights was already known by Roman law (ususfructus nominis) for the admission of usufruct over patrimonies, but it is a controversial question on which our doctrine has not yet managed to reach a peaceful position. Immediately another aspect of our research is represented: its broad spectrum. In effect, the proposed topic is projected on very broad sectors of legal science. On the one hand, the right of usufruct, a civil law institution widely studied. But on the other hand, the truth is that, having a right of usufruct over social actions or participations, the usufruct is capable of displaying its effects on all the institutions of the corporate phenomenon. The purpose of this work is to study the usufruct of social actions and participations. It is an institution whose importance can not be minimized, from the point and time that the Spanish legislator (common and regional) makes a wide use of usufruct in family and inheritance institutions. This means that many of these rights are born every day, from the point and time of the well-known phenomenon of the increase in the personal wealth of individuals and families. In fact, it should not be ignored that although at other times wealth was fundamentally real estate or pecuniary, in ours the savings of private individuals are channeled in a decisive way through corporate instruments. In the same way, more and more, even small companies tend to adopt corporate forms, and a very important part of saving (especially in the current situation of low interest rates) is placed in the stock markets, either directly, or through institutions of collective investment that often adopt corporate forms. This proposition immediately refers to a very broad list of legal institutions. On the one hand, we are dealing with real rights, a category traditionally opposed to credit rights. However, the object usufructuado is far from being a corporeal thing, but are the actions and social participations, whose nature has been controversial matter. However, the possibility of incorporating shares in securities determines that the usufruct over tangible things can not be excluded without further ado. At the same time, the shares are susceptible to being represented by book entries (which is now mandatory for their quotation in the stock markets), implying a special regime. Therefore, it seems that the study of the proposed topic should start with a few reflections on the nature of real rights, distinguishing ownership of limited real rights, and, in particular, the phenomenon of usufruct rights, both real and personal. The possibility of usufruct over credit rights was already known by Roman law (ususfructus nominis) for the admission of usufruct over patrimonies, but it is a controversial question on which our doctrine has not yet managed to reach a peaceful position. Immediately another aspect of our research is represented: its broad spectrum. In effect, the proposed topic is projected on very broad sectors of legal science. On the one hand, the right of usufruct, a civil law institution widely studied. But on the other hand, the truth is that, having a right of usufruct over social actions or participations, the usufruct is capable of displaying its effects on all the institutions of the corporate phenomenon.El propósito de este trabajo es estudiar el usufructo de acciones y participaciones sociales. Se trata de una institución cuya importancia no puede ser minimizada, desde el punto y hora de que el legislador español (común y foral) hace una amplísima utilización del usufructo en las instituciones familiares y sucesorias. Ello determina que todos los días nazcan multitud de estos derechos, desde el punto y hora del conocido fenómeno del incremento de la riqueza mobiliaria de las personas y de las familias. En efecto, no cabe desconocer que si bien en otros tiempos la riqueza era fundamentalmente inmobiliaria o pecuniaria, en los nuestros el ahorro de los particulares se canaliza de forma determinante a través de instrumentos societarios. Del mismo modo, cada vez más, incluso las pequeñas empresas tienden a adoptar formas societarias, y una parte muy importante del ahorro (especialmente en la actual coyuntura de bajos tipos de interés) se coloca en los mercados bursátiles, bien directamente, bien mediante instituciones de inversión colectiva que, con frecuencia, adoptan formas societarias. Tal proposición remite inmediatamente a un elenco muy amplio de instituciones jurídicas. Por una parte nos encontramos con el ámbito de los derechos reales, categoría tradicionalmente contrapuesta a los derechos de crédito. Sin embargo el objeto usufructuado dista de ser una cosa corporal, sino que son las acciones y participaciones sociales, cuya naturaleza ha sido materia controvertida. No obstante la posibilidad de incorporar las acciones a títulos determina que no pueda ser excluido sin más el usufructo sobre cosas corporales. Al mismo tiempo las acciones son susceptibles de ser representadas mediante anotaciones en cuenta (lo que hoy día es obligatorio para su cotización en los mercados bursátiles), implicando un régimen especial. Por lo tanto parece que el estudio del tema propuesto debe comenzar con unas breves reflexiones sobre la naturaleza de los derechos reales, distinguiendo la propiedad de los derechos reales limitados, y, en especial, del fenómeno del usufructo sobre derechos, tanto reales como personales. La posibilidad del usufructo sobre derechos de créditos fue ya conocida por el Derecho romano (ususfructus nominis) por la admisión del usufructo sobre patrimonios, pero es una controvertida cuestión sobre la que nuestra doctrina no ha conseguido aún alcanzar una posición pacífica. Inmediatamente se representa otro aspecto de nuestra investigación: su amplio espectro. En efecto el tema propuesto se proyecta sobre sectores muy amplios de la ciencia jurídica. Por una parte, el derecho de usufructo, institución de Derecho civil ampliamente estudiada. Pero por otra, lo cierto es que, existiendo un derecho de usufructo sobre las acciones o participaciones sociales, el usufructo es susceptible de desplegar sus efectos sobre todas las instituciones del fenómeno societario. Así pueden verse implicados el proceso de formación social, las modificaciones estructurales, las modificaciones estatutarias, la determinación y aplicación del resultado social, el proceso de formación de la voluntad social, la impugnación de acuerdos sociales, la disolución, liquidación y extinción de la sociedad, etc. Tal amplitud obliga, evidentemente, atendida la naturaleza de este trabajo, a realizar una limitación metodológica. No se pretende examinar exhaustivamente todos los aspectos y posibilidades del usufructo. Al mismo tiempo tampoco se trata de implementar una revisión de todo el derecho de sociedades cuando concurre un usufructo. El objetivo, más modesto, se centra en estudiar el fenómeno usufructuario en cuanto puede tener relevancia sobre los más importantes aspectos de la vida social.