Spanish Abstract: La brecha fiscal es un concepto de importancia creciente en el ambito de las administraciones tributarias que indica la diferencia entre la recaudacion impositiva efectiva y la que deberia obtenerse de haber un cumplimiento fiscal perfecto. Su estimacion ofrece una informacion muy relevante sobre el tamano relativo y la naturaleza del incumplimiento fiscal, asi como sobre su evolucion a lo largo del tiempo. En este articulo se destaca su utilidad como herramienta de gestion de la propia administracion tributaria y para mejorar su rendicion de cuentas ante la sociedad, senalandose tambien sus posibles debilidades metodologicas y las cauciones a la hora de interpretar sus resultados. Asimismo, se presenta la metodologia y los resultados obtenidos al estimar la brecha fiscal de Cataluna, a partir de microdatos de los tres impuestos relacionados con la riqueza (patrimonio, sucesiones y transmisiones) mas importantes que administran las comunidades autonomas espanolas de regimen comun. English Abstract: The tax gap can be defined as the difference between the total amount of taxes collected by tax authorities and the total tax revenues that should be collected according to the tax code and under perfect tax compliance. The estimation of the tax gap offers very useful information about the relative size and nature of non-compliance, as well as its evolution over time. In this paper we point out that the tax gap is a valuable instrument not only to define the enforcement strategies of the tax administration but also to enhance the accountability of this public authority. Nonetheless, the methodology employed to estimate the tax gap and consequently the interpretation of the results of this assessment are subject to limitations that are discussed in the paper. Moreover, we present the methodology to estimate the tax gap in Catalonia for the three most important taxes related to wealth (wealth tax, inheritance and gift tax and transfer tax) administered by the Spanish regions and, finally, we provide the results from the estimations obtained employing microdata.