  The MEG experiment took data at the Paul Scherrer Institute in the years
2009--2013 to test the violation of the lepton flavour conservation law, which
originates from an accidental symmetry that the Standard Model of elementary
particle physics has, and published the most stringent limit on the charged
lepton flavour violating decay ${\mu}^+ \rightarrow {\rm e}^+ \gamma$:
BR(${\mu}^+ \rightarrow {\rm e}^+ \gamma$) $<4.2 \times 10^{-13}$ at 90%
confidence level. The MEG detector has been upgraded in order to reach a
sensitivity of $6\times10^{-14}$. The basic principle of MEG II is to achieve
the highest possible sensitivity using the full muon beam intensity at the Paul
Scherrer Institute ($7\times10^{7}$ muons/s) with an upgraded detector. The
main improvements are better rate capability of all sub-detectors and improved
resolutions while keeping the same detector concept. In this paper, we present
the current status of the preparation, integration and commissioning of the MEG
II detector in the recent engineering runs.
