We introduce a new photometric catalog of RR Lyrae (RRL) variables (∼300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and blue horizontal branch (BHB) stars ever collected. This includes radial velocity measurements (∼16,000) and iron abundances (∆S method for 8140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated with the main Galactic components and their iron distribution function (IDF) becomes more metal rich when moving from the halo ([Fe/H] = −1.56) to the thick disk (TCD; [Fe/H] = −1.47) and thin disk (TND; [Fe/H] = −0.73). Furthermore, halo RRLs and RRLs in retrograde orbits are α enhanced ([α/Fe]=0.27, σ = 0.18), while TCD RRLs are either α enhanced ([Fe/H] ≤ −1.0) or α poor ([Fe/H] > −1.0), and TND RRLs are mainly α poor ([α/Fe] = −0.01, σ = 0.20). We also identified RRLs associated with the main stellar streams—Gaia─Sausage─Enceladus (GSE); Sequoia, Helmi, and Sagittarius—and we found that their IDFs are quite similar to halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their α-element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD, and halo RRLs is negative and it decreases from −0.026, to −0.010, and to −0.002 dex kpc−1. The iron radial gradient based on dry halo (halo without substructures) RRLs is, within the errors, equal to the global halo. We also found a strong similarity between iron and [α/Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples. *Based in part on observations made with the Southern African Large Telescope (SALT): Program IDs: 2017-2-SCI-041, 2018-1-SCI-018, 2018-2-SCI-025, 2019-1-SCI-013, 2021-2-SCI-028, 2022-2-DDT-001, PI: B. Chaboyer). Based in part on data obtained in the Observatorios de Canarias del Instituto de Astrofisica de Canarias (IAC) with: the STELLA robotic telescope, an AIP facility jointly operated by AIP and IAC at the Teide Observatory in Tenerife, Spain; the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei of the INAF, the Nordic Optical Telescope (NOT) owned in collaboration by the University of Turku and Aarhus University and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University, and the Mercator telescope operated by the Flemish Community, all at the Observatorio del Roque de los Muchachos of the IAC, La Palma, Spain (Program IDs: 101-MULTIPLE-4/21B, 107-MULTIPLE-4/22A, 120-MULTIPLE-2/23B, 165-Stella12/20A, PI: M. Monelli; Program ID: 108-MULTIPLE-2/25B, PI: M. Sánchez-Benavente).