Zilean Runes explained
There's one set of runes for Zilean on patch
11.20
that is the clear favorite for LoL players and pros alike. The best Zilean Runes on the position 
Support are Sorcery as the primary path and
Inspiration as the secondary path with a pick rate of 49%. Besides runes you should take a look on Zilean Build and if you are interested in pro matches take a look at Zilean Probuilds. If you want to discuss
Zilean then you should visit the champion subreddit.
Primary path on Zilean
Sorcery empoweres abilities of Zilean and increases the available champion resources. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Summon Aery is the best keystone rune to run on
Zilean. This keystone rune adds more poke damage to your abilities. And additionally grants an extra shield, whenever Zilean empowers or protects an ally with abilities. This is usually followed up by taking
Manaflow Band,
Transcendence and
Scorch.
This is usually followed up by taking
Manaflow Band for additional mana and mana regenaration.
Transcendence for some more Ability Haste.
Scorch increases your control in the early game.
Secondary path on Zilean
When it comes to your secondary path, most
Zilean players prefer to go with
Inspiration.
Inspiration opens creative opportunities on Zilean troughout the match. On the
Inspiration path, the best runes for Zilean are
Biscuit Delivery and
Cosmic Insight.
Biscuit Delivery is a great rune for laning as it gives additional health and mana, which can help in more aggressive lanes.
Cosmic Insight grants summoner spell and item haste.
FAQ for Zilean Runes
Which is the best keystone rune on Zilean?
The best keystone rune on Zilean is
Summon Aery.