In this chapter, the structure of (polypropylene) PP fibers was evaluated systematically and comparatively using different processing conditions via melt blowing. The influence of four parameters (air pressure, air temperature, die-to-collector distance (DCD), and collector speed) on the fiber morphology (fiber diameter, pore size, porosity) and mechanical and thermal properties were detailed and the fiber formation mechanism was investigated. Melting temperature, melting enthalpy and crystallinity were obtained using the differential scanning calorimetry (DSC) technique as a function of melt-blowing parameters. The crystallite size and crystal phase evaluations were carried out using the peak parameters obtained by the curve fitting of the equatorial wide-angle X-ray diffraction (WAXD) profiles. A new factor, the mat consolidation coefficient, was introduced and used to efficiently summarize melt-blown (MB) PP fiber mats’ process-property-structure relationships. This study details how to control the melt blowing parameters to tailor the PP fiber mat features for the respective application fields. It also gives insight into fiber formation mechanisms during melt blowing to generate self-bonded, defect-free, fine fiber mats.