  Attosecond science has opened up new frontiers in our understanding of
processes happening on the intrinsic timescale of electrons. The ability to
manipulate and observe phenomena at the attosecond level has yielded
groundbreaking insights into processes such as electron dynamics and the
behavior of matter under extreme conditions. This interdisciplinary field
bridges various research areas such as quantum optics, quantum chemistry and
quantum information science facilitating a cohesive understanding. However,
despite many emerging successful applications, the discussion about intrinsic
quantum effects has mainly been ignored. In this Perspective, we explore the
latest advancements in quantum phenomena within attosecond science,
encompassing both experimental and theoretical progress. Specifically, in the
context of high-harmonic generation and above-threshold ionization, we focus on
discerning genuinely quantum observations and distinguishing them from
classical phenomena. Additionally, we illuminate the often overlooked yet
significant role of entanglement in attosecond processes, elucidating its
influence on experimental outcomes.
