Runes can only be purchased from the Riot Store with Influence Points. Runes cannot be purchased with Riot Points. Each rune grants a small bonus in a specific category, which stack upon each other to grant larger bonuses.
Glyphs, marks, and seals stack up to 9 for increased effect, and quintessences stack up to 3.
Purchasing the maximum useful number of every type of tier 3 rune (9 of each glyph, mark and seal, and 3 of each quintessence) would cost 397,620 IP, encouraging specialization.
It is also important to note that some runes are "primary", while others are called "secondary" and provide lesser bonuses. Given a certain kind of rune, it will be primary in either marks, glyphs or seals, and secondary in the other two rune types. So, all kind of runes have one primary type for them and two secondary types. The aura shrouding a rune of a certain effect will denote which rune type it is considered primary - for example, ability power runes will have a blue aura showing that it is Glyphs that specialise in them.
Although Quintessences have the max possible effect, you may only have three instead of the nine marks, seals, or glyphs - this means one quintessence should be equal to three or more runes in order to qualify as a "Primary" Quintessence. The following Quintessences have an effect equal to or greater than three primary runes:
The Tier of a rune represents its relative power (i.e. the extent of the bonuses it offers), and is visible in the top-left of the pop-up when mousing over it.
Tier 1 or "Lesser" runes are dark and faded with visible scratches and chips except for Quintessences, which are simply purple.
Tier 2 don't have prefixes, they are slightly brighter and are not tattered; Quintessences now have gold faces and purple backgrounds. You can buy them starting at level 10.
Tier 3 or "Greater" runes are brightly lit; Quintessences are completely covered in gold. You can buy them starting at level 20.
It is important to note that you cannot buy a Tier 3 rune before you reach level 20, and that you can acquire random ones for less IP than buying them outright by using the Rune Combiner.
Five "Lesser Seals of Mana Regeneration" cost 75 IP (5 × 15 IP), while one "Seal of Replenishment" costs 80. This equates to a saving of 5 IP.
Likewise, a combined Tier 3 rune would cost 375 IP (25 × 15 = 5 × 75), cheaper than Tier 3 runes of costs from 410 to 2050 IP. This equates to a saving of 35 IP minimum and 1675 IP maximum.
The cheapest Tier 3 rune costs 205. This equates to a 170 IP loss.
Keep in mind that combining 5 runes of one type will not guarantee you a better (Primary) rune of that same type. The Rune Combiner may also give you a Secondary Rune.
It is possible to combine runes to higher tiers and use them freely even if you are too low a level to buy them directly. However, it is not recommended, as most runes aren't that helpful (e.g. hybrid penetration runes, which are very specific, or secondary runes), thus the best long term strategy is to start buying them at level 20 and saving up Influence Points before then.
Summoners are able to use a rune per level of power in League of Legends, and they keep their Runes in a tome called a Runebook. Before a match begins, a Summoner will be able to choose from up to twenty different rune configurations they have previously set in their Runebook. This allows the Summoner to have quick flexibility in choosing a Runebook configuration best suited for whatever champion they might use in any of Valoran's Fields of Justice.