The so-called Marshrutnoje Taxi, also known as Marshrutka, is a small van for a maximum of 10 people, and it is a quite common means of transportation in Irkutsk. Basically speaking, it works the same way as the regular public transportation: the Marshrutka is bound to its route (usually, similar to routes of regular public transportation) which includes defined stopping-places. A schedule with all lines does exist; however, it is rather hard to understand. According to our experience, the people of Irkutsk are very helpful, so asking for the right line might be the best way. Besides, the basic routes are written on the Marshrutkas. Once you found the right cab, you can ask the driver to let you out at your desired stop: "mikrochirurgia ostanawitje, poshaluista" ("stop at 'Mikrochirurgia', please"). It always worked for us. If you know where you want to get out, you can do as the people of Irkutsk do and call out "ostanawitje na sljeduschi" ("stop at the next point") to the driver; otherwise, he will drive past the stop.
The payment will be made when leaving the cab. One ride, no matter how far it is, currently costs 8 Rbl. During daytime, the Marshrutkas run in very short intervals. There are no fixed departure times. But starting at 11pm, you should hurry, because for security reasons most cabs only run till midnight. And the next one won't depart until approx. 7am.
And another hint: If you have to get to a destination outside of Irkutsk but you don't know how to get there, or there is no train, or the tickets for the bus are all sold-out, then you should negotiate with the drivers of the Marshrutkas. For a fixed price, they will take you to your destination, wait there for a few hours if necessary, and then take you back.