sudo apt-get install wpasupplicant

# Debian 8 "Jessie"
deb http://http.debian.net/debian/ jessie main contrib non-free

apt-get update && apt-get install firmware-iwlwifi

modprobe -r iwlwifi ; modprobe iwlwifi

nano /etc/network/interfaces

auto wlan0
iface wlan0 inet dhcp
wpa-ssid YOUR-SSID-HERE
wpa-psk YOUR-PASSWORD-HERE

ifup wlan0

/etc/init.d/networking restart