The increase of the instantaneous luminosity at the
High-Luminosity LHC (HL-LHC, phase 2)
places stringent requirements on the detectors.
New proposed calorimeters have to be designed to operate
in the harsh radiation environment at the HL-LHC,
where the average number of interactions per bunch crossing is
expected to exceed 140.
The LHC experiments have proposed various high-granularity
calorimetric solutions.
In this talk, I focus on the new CMS high-granularity calorimeter (HGCAL),
a highly granular sampling calorimeter with approximately six million silicon sensor channels
($\simeq$ 0.5 cm$^2$ and 1.1 cm$^2$ cells) and about four hundred thousand
scintillator tiles read out by on-tile silicon photomultipliers.
The HGCAL electronics, besides measuring energy and position of the energy deposits,
are also designed to measure the time of particle arrival with a
precision of about 50 ps. In HGCAL, we have developed a
reconstruction approach that fully exploits the granularity to achieve
optimal electron, photon and hadron identification, as well as
good energy resolution in the presence of pileup.