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There are additional reasons to search for and study massive BHs in dwarf galaxies. The radiation from high-redshift BHs in this mass range may impact reionization and the formation of the first galaxies (e.g., Milosavljevi\'{c} et al. 2009). Moreover, the study of BH accretion and star formation in low-mass dwarfs today may prove a good laboratory for understanding their interplay at early times (e.g., Reines et al. 2011) and the apparent contribution of obscured AGN in blue low-mass galaxies to the cosmic X-ray background (Xue et al. 2012). Determining the presence and impact of AGN in low-mass galaxies will also help constrain BH feedback and galaxy formation models at all mass scales.  Until recently, however, very few dwarf galaxies were known to host massive BHs. The prototypical examples are NGC 4395, a dwarf spiral, and Pox 52, a dwarf elliptical. Both galaxies exhibit clear AGN signatures and the BH masses are estimated to be $M_{\rm BH} \sim 3\times 10^5 M_{\odot}$ (e.g., Filippenko & Ho 2003; Barth et al. 2004; Peterson et al. 2005). Reines et al. (2011) found multi-wavelength evidence for the first example of a massive BH in a dwarf starburst galaxy, Henize 2-10, including Chandra and VLA point sources. Follow-up VLBI observations reveal parsec-scale non-thermal radio emission from the active nucleus (Reines & Deller 2012). Systematic searches for active low-mass BHs have revealed > 200 galaxies with MBH <⇠ 106.5 M $M_{\rm BH} \leq 10^{6.5} M_{\odot}$  (Greene & Ho 2007; Dong,X.-B. et al. 2012), however the vast majority of the galaxies in these samples are larger and more massive than typical dwarf galaxies (Greene et al. 2008; Jiang et al. 2011; Dong,X.-B. et al. 2012). We have undertaken the first systematic search for AGN in dwarf galaxies with stellar masses less than or comparable to the Large Magellanic Cloud (LMC), increasing the number of known dwarfs hosting massive BHs by an order of magnitude (Reines et al. 2013).