How to install Mono 4.0.1 on Debian 8?

I resolved this by following article posted by Alexander but also installed one more package monodevelop.

Following commands i run to install mod mono on debian 8.0 jessie:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb http://download.mono-project.com/repo/debian wheezy main" | sudo tee /etc/apt/sources.list.d/mono-xamarin.list
sudo apt-get update

echo "deb http://download.mono-project.com/repo/debian wheezy-apache24-compat main" | sudo tee -a /etc/apt/sources.list.d/mono-xamarin.list

echo "deb http://download.mono-project.com/repo/debian wheezy-libjpeg62-compat main" | sudo tee -a /etc/apt/sources.list.d/mono-xamarin.list

sudo apt-get update

sudo apt-get install mono-complete

To get development IDE run:

sudo apt-get install monodevelop

After then can successfully run : sudo a2enmod mod_mono_auto

There was an issue with the Mono packages that should now be resolved, please see http://www.mono-project.com/docs/getting-started/install/linux/#libgdiplus-debian-80-and-later-not-ubuntu.

The reason is that Debian 8 doesn't have libjpeg8 anymore which libgdiplus (a component of Mono) requires.