  The interaction of antikaons with nucleons and nuclei in the low-energy
regime represents an active research field in hadron physics with still many
important open questions. The investigation of light kaonic atoms, in which one
electron is replaced by a negatively charged kaon, is a unique tool to provide
precise information on this interaction; the energy shift and the broadening of
the low-lying states of such atoms, induced by the kaon-nucleus hadronic
interaction, can be determined with high precision from the atomic X-ray
spectroscopy, and this experimental method provides unique information to
understand the low energy kaon-nucleus interaction at the production threshold.
The lightest atomic systems, like the kaonic hydrogen and the kaonic deuterium
deliver, in a model-independent way, the isospin-dependent kaon-nucleon
scattering lengths. The most precise kaonic hydrogen measurement to-date,
together with an exploratory measurement of kaonic deuterium, were carried out
in 2009 by the SIDDHARTA collaboration at the DA{\Phi}NE electron-positron
collider of LNF-INFN, combining the excellent quality kaon beam delivered by
the collider with new experimental techniques, as fast and very precise X-ray
detectors, like the Silicon Drift Detectors. The SIDDHARTA results triggered
new theoretical work, which achieved major progress in the understanding of the
low-energy strong interaction with strangeness reflected by the
antikaon-nucleon scattering lengths calculated with the antikaon-proton
amplitudes constrained by the SIDDHARTA data. The most important open question
is the experimental determination of the hadronic energy shift and width of
kaonic deuterium; presently, a major upgrade of the setup, SIDDHARTA-2, is
being realized to reach this goal. In this paper, the results obtained in 2009
and the proposed SIDDHARTA-2 upgrades are presented.
