Attosecond pulse trains (APT) emerged from high harmonics (Anne L’Huillier et al, 1987) and their spectral phase determination by RABBITT (Pierre-Marie Paul et al, 2001). Although the record of the shortest pulse of 43 as belongs to the technique of isolated attosecond pulse (IAP), APT and RABBITT have been extremely popular over the last 20 years. In this talk I will briefly review the physics involved in both as well as some applications at Ohio-State including photoionization delays, and the recent timing of non- sequential double ionization. In conclusion I will evoke the advent of zeptoseconds in photoionization delays and the future of attosecond science high- power IAP at free-electron laser.