This chapter deals with the automated and unattended design of planar wideband bandpass filters by means of aggressive space mapping (ASM) optimization. The approach can be applied to bandpass filters based on semi-lumped element resonators (e.g., stepped impedance resonators, ring resonators, etc.) coupled through admittance inverters (implemented with quarter-wavelength transmission lines). It will be explained how the filter layout is automatically generated from filter specifications, i.e., central frequency, fractional bandwidth, in-band ripple, and order, without the need of any external aid to the design process. For this purpose, a novel optimization algorithm based on two independent ASM processes will be fully described. The proposed automatic design procedure will be detailed and validated through its application to generate several filter layouts starting from different sets of practical specifications.