Planck CollaborationAghanim, N.N.AghanimAkrami, Y.Y.AkramiMigliaccio, M.M.MigliaccioNatoli, PaoloPaoloNatoliPolenta, GianlucaGianlucaPolenta2020-09-172020-09-172018-07-01https://hdl.handle.net/20.500.13025/5642eprint arXiv 1807.06210We present measurements of the cosmic microwave background (CMB) lensing potential using the final $textit{Planck}$ 2018 temperature and polarization data. We increase the significance of the detection of lensing in the polarization maps from $5,sigma$ to $9,sigma$. Combined with temperature, lensing is detected at $40,sigma$. We present an extensive set of tests of the robustness of the lensing-potential power spectrum, and construct a minimum-variance estimator likelihood over lensing multipoles $8 le L le 400$. We find good consistency between lensing constraints and the results from the $textit{Planck}$ CMB power spectra within the $rm{Lambda CDM}$ model. Combined with baryon density and other weak priors, the lensing analysis alone constrains $sigma_8 Omega_{rm m}^{0.25}=0.589pm 0.020$ ($1,sigma$ errors). Also combining with baryon acoustic oscillation (BAO) data, we find tight individual parameter constraints, $sigma_8=0.811pm0.019$, $H_0=67.9_{-1.3}^{+1.2},text{km},text{s}^{-1},rm{Mpc}^{-1}$, and $Omega_{rm m}=0.303^{+0.016}_{-0.018}$. Combining with $textit{Planck}$ CMB power spectrum data, we measure $sigma_8$ to better than $1,%$ precision, finding $sigma_8=0.811pm 0.006$. We find consistency with the lensing results from the Dark Energy Survey, and give combined lensing-only parameter constraints that are tighter than joint results using galaxy clustering. Using $textit{Planck}$ cosmic infrared background (CIB) maps we make a combined estimate of the lensing potential over $60,%$ of the sky with considerably more small-scale signal. We demonstrate delensing of the $textit{Planck}$ power spectra, detecting a maximum removal of $40,%$ of the lensing-induced power in all spectra. The improvement in the sharpening of the acoustic peaks by including both CIB and the quadratic lensing reconstruction is detected at high significance (abridged).Astrophysics - Cosmology and Nongalactic Astrophysics Comment Submitted to A&A. Abstract abridged for arxiv submission. Lensing data products available at https //wiki.cosmos.esa.int/planck-legacy-archive/index.php/Lensinghttp://adsabs.harvard.edu/abs/2018arXiv180706210P2018arXiv180706210P