Katarina Runes explained
There's one set of runes for Katarina on patch 15.12 that is the clear favorite for LoL players and pros alike. The best Katarina rune paths on the position 
Mid are 
Domination as the primary path and 
Inspiration as the secondary path with a pick rate of 69%. Besides picking runes on Katarina you should learn how to play Katarina and if you are interested in pro matches take a look on how a pro builds Katarina. If you want to discuss 
Katarina then you should visit the champion subreddit.
Katarina runes from primary path
Domination improves burst damage and assassination tools on Katarina. Most of high elo players – and our LoL pros in the the major regions – have agreed that 
Electrocute is the best keystone rune to run on Katarina. This keystone rune provides burst damage, aiding them in nuking down the enemy carries. Other primary runes on Katarina are 
Sudden Impact, 
Grisly Mementos and 
Relentless Hunter.
Sudden Impact increases your damage after dashing or being invisible. This is due to how easy it is to activate on Katarina with the amount of ways he has to dash, jump or going invisible. The additional lethality helps to take down the priority targets that much easier. Relentless Hunter increases your movement speed out of combat due to every unique champion takedown.
Katarina runes from secondary path
When it comes to your secondary path, most Katarina players prefer to go with Inspiration. Inspiration opens creative opportunities on Katarina troughout the match. On the Inspiration path, the best runes for Katarina are 
Cosmic Insight and 
Biscuit Delivery.
Cosmic Insight grants summoner spell and item haste. Biscuit Delivery is a great rune for laning as it gives additional health and mana, which can help in more aggressive lanes.
FAQ for Katarina Runes
Which is the best keystone rune on Katarina?
The best keystone rune on Katarina is Electrocute. This Katarina runes setup is then referred as Katarina Electrocute.
What runes does Katarina use?
Runes from the paths Domination and Inspiration are the most used runes on Katarina. For the exact pick rates of Katarina runes used, you have to study the rune distribution presented.