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In this work we investigate the stability and instability properties of aclass of naked singularity spacetimes. The first rigorous study of nakedsingularity formation in the spherically symmetric Einstein-scalar field systemwas due to Christodoulou, who constructed a family $(\overline{g}_k,\overline{\phi}_k)$ of $k$-self-similar solutions, for any $k^2 \in(0,\frac{1}{3})$. We extend the construction to produce examples of interiorand exterior regions of naked singularity spacetimes locally modeled on the$(\overline{g}_k, \overline{\phi}_k)$, without requiring exact self-similarity.  The main result is a global stability statement under fine-tuned dataperturbations, for a class of naked singularity spacetimes satisfyingself-similar bounds. Given the well-known blueshift instability for suitablyregular naked singularities in the Einstein-scalar field model, we requirenon-generic conditions on the data perturbations. In particular, the scalarfield perturbation along the past lightcone of the singular point $\mathcal{O}$vanishes to high order near $\mathcal{O}$. Technical difficulties arise fromthe singular behavior of the background solution, as well as regularityconsiderations at the axis and past lightcone of the singularity. The interiorregion is constructed via a backwards stability argument, thereby avoidingactivating the blueshift instability. The extension to the exterior region istreated as a global existence problem to the future of $\mathcal{O}$, adaptingtechniques of Rodnianski and Shlapentokh-Rothman for vacuum spacetimes.

A construction of approximately self-similar naked singularities for the spherically symmetric Einstein-scalar field system