We present an unifying description close to a spatial bifurcation of localized states, appearing as large amplitude peaks nucleating over a pattern of lower amplitude. Localized states are pinned over a lattice spontaneously generated by the system itself. We show that the phenomenon is generic and requires only the coexistence of two spatially periodic states. At the onset of the spatial bifurcation, a forced amplitude equation is derived for the critical modes, which accounts for the appearance of localized peaks. In one-dimensional systems, localized patterns can be described as homoclinic orbits passing close to a spatially oscillatory state and converging to an homogeneous state [9,10], whereas domains are seen as heteroclinic trajectories joining the fixed points of the corresponding dynamical system [11]. Recently, in a nematic liquid crystal light valve with optical feedback it has been found experimentally a different type of localized states, appearing as a large amplitude peaks nucleating over a lower amplitude pattern and therefore called localized peaks [12]. Similar observations have been reported in a Newtonian fluid when non linear surface waves are parametrically excited with two frequencies [13] and in numerical simulations of an atomic vapor with optical feedback [14]. Recently, longitudinal modes with localized peaks over a spatially modulated background have been shown in numerical simulations of Maxwell-Bloch equations for a semiconductor laser [15].All these different types of localized states appear over a patterned background and thus constitute a different class of structures with respect to the ones appearing over an uniform background. The aim of this manuscript is to show that localized peaks are a generic class of localized states, appearing whenever a pattern forming system exhibits coexistence of two spatially periodic states. The mechanisms that originate this circumstances are more than a few, for instance, one can consider a multi-stable system, which shows two consecutive spatial bifurcations to different states when one parameter is changed. There is a large number of physical systems that display this kind of behavior, therefore there is a vast number of possible models. In order to derive an unifying and simple description of localized peaks, we develop a theoretical model for one-dimensional spatially extended systems close to a spatial bifurcation. The model, which shows coexistence between different patterns and stable front solutions between them, is based on an amplitude equation that includes a spatial parametric forcing. This extension with respect to conventional amplitude equations, allows to describe localized patterns and to account for the main properties of these solutions. The model includes the interaction of the slowly varying envelope with the small scale of the underlying pattern solution [16], well-known as the non-adiabatic effect [17,18].