  In the past twenty years, we have reached a broad understanding of many
light-driven phenomena in nanoscale systems. The temporal dynamics of the
excited states are instead quite challenging to explore, and, at the same time,
crucial to study for understanding the origin of fundamental physical and
chemical processes. In this review we examine the current state and prospects
of ultrafast phenomena driven by plasmons both from a fundamental and applied
point of view. This research area is referred to as ultrafast plasmonics and
represents an outstanding playground to tailor and control fast optical and
electronic processes at the nanoscale, such as ultrafast optical switching,
single photon emission and strong coupling interactions to tailor photochemical
reactions. Here, we provide an overview of the field, and describe the
methodologies to monitor and control nanoscale phenomena with plasmons at
ultrafast timescales in terms of both modeling and experimental
characterization. Various directions are showcased, among others recent
advances in ultrafast plasmon-driven chemistry and multi-functional plasmonics,
in which charge, spin, and lattice degrees of freedom are exploited to provide
active control of the optical and electronic properties of nanoscale materials.
As the focus shifts to the development of practical devices, such as
all-optical transistors, we also emphasize new materials and applications in
ultrafast plasmonics and highlight recent development in the relativistic
realm. The latter is a promising research field with potential applications in
fusion research or particle and light sources providing properties such as
attosecond duration.
