Context : The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields .
It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution .
The survey will ultimately uncover several hundreds of galaxy clusters out to a redshift of \sim 2 at a sensitivity of \sim 10 ^ { -14 } erg s ^ { -1 } cm ^ { -2 } in the [ 0.5-2 ] keV band .

Aims : This article presents the XXL bright cluster sample , a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of 3 \times 10 ^ { -14 } erg s ^ { -1 } cm ^ { -2 } on the source flux within a 1 ^ { \prime } aperture .

Methods : The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process .
An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters .
We derived accurate X-ray parameters for all the sources .
Scaling relations were self-consistently derived from the same sample in other publications of the series .
On this basis , we study the number density , luminosity function , and spatial distribution of the sample .

Results : The bright cluster sample consists of systems with masses between M _ { 500 } = 7 \times 10 ^ { 13 } and 3 \times 10 ^ { 14 } M _ { \odot } , mostly located between z=0.1 and 0.5 .
The observed sky density of clusters is slightly below the predictions from the WMAP9 model , and significantly below the prediction from the Planck 2015 cosmology .
In general , within the current uncertainties of the cluster mass calibration , models with higher values of \sigma _ { 8 } and/or \Omega _ { M } appear more difficult to accommodate .
We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to z \sim 1 .
We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters .

Conclusions :