A big part of genealogical researchers use the STATE REGIONAL ARCHIVES. Their addresses are:
(for the middle part of Bohemia)

Statni oblastni archiv
Archivní ulice 4
149 01 Praha

brach offices in: Benesov u Prahy, Mnichovo Hradiste

(for the northern Bohemia)

Statni oblastni archiv
Krajska 1
412 74 Litomerice

brach offices in: Decin, Jablonec nad Nisou, Zitenice

(for the western Bohemia)

Statni oblastni archiv
Sedlackova 44
306 12 Plzen

brach offices in: Klatovy, Zlutice

(for the southern Bohemia)

Statni oblastni archiv
Zamek 1
379 11 Trebon

brach offices in: Ceske Budejovice, Cesky Krumlov, Jindrichuv Hradec

(for the eastern Bohemia)

Statni oblastni archiv
Zamek 1
565 43 Zamrsk

(for the northern Moravia)

Zemsky archiv
Wurmova 11
771 11 Olomouc

brach offices in: Janovice u Rymarova

(for the southern Moravia)

Moravsky zemsky archiv
Zerotinovo nam. 3 / 5
656 01 Brno

brach offices in: Kunstat, Kromeriz

(for the Silesia)

Zemsky archiv
Snemovni 1
746 22 Opava

In the archives above you can find the registers of births, marriages, deaths; materials of county offices, manors. Some archives suffer from a lack of space so some materials were moved to branch-offices.

To obtain more detailed data on your found ancestors, researchers visit the STATE CENTRAL ARCHIVES in Praha, and the LAND ARCHIVES in Brno. The following materials are stored there: cadastres, old maps, documents of the government, Jewish registers (in Praha), archiepiscopal documents. The Land archives in Brno contain the materials mentioned in STATE REGIONAL ARCHIVES as well. The State central archives in Praha is devided into two departments:
(the oldest materials up to 1850)

Statni ustredni archiv
Milady Horakove 133
160 00 Praha 6

(from 1850 up to this day)

Statni ustredni archiv
Archivní ulice 4
149 01 Praha

Very important are also the STATE DISTRICT ARCHIVES. They are found in the previous centres of the political districts and cover areas of those districts. You can find there: chronicles, local literature, city registers, address-books, censuses of inhabitants, church records, emigration records, pictures, school records, cemetery registers.

We should mention the MILITARY HISTORICAL ARCHIVES too. You can search in different materials of regiments, personal documents that were kept on every soldier. Address:

Vojenský historický archiv
Sokolovska 136
186 00 Praha 8

In some cases it is useful to visit the archives kept by factories and Universities. Then you can enrich your knowledges by data consisted in personal documents that were kept on every worker or student.