According to Sony:
"In order to continue bringing you the best online games experience on PSN, we will perform routine maintenance beginning the morning of Monday, April 15th. This maintenance will start at approximately 8:00AM PT (9:00AM MT / 10:00AM CT / 11:00 AM ET) and last until around 8:00PM PT (9:00PM MT / 10:00PM CT / 11:00PM ET)"
The PlayStationNetwork should be down for around 12 hours but Sony says that if you sign in to the network before the maintainance period, you should be able to still play games online and apps, so make sure to sign in now!
Have you been affected by the network going down? Let us know about it in the comments below!