Dagome Iudex is a common name for one of the earliest written documents related to Poland, written originally in around 991/2. Its name came from first two words of document. One should be warned that Dagome iudex is not the original, but a summary of it, done around 1080 (it was found in a register made by one of the curial cardinals from the time of pope Gregory VII). Names of places are terribly mangled by the monk who made the summary. That monk did not even realise that document was related to Poland.
The document is very important for Polish history, since it contains a description of the Polish state at the time. There are also many puzzles in the document. First, why did Mieszko I give his state to Pope? Second, why isn't Boleslaw I Chrobry, the oldest son of Mieszko even mentioned, but instead his sons from second marriage and his second wife are mentioned? Third, why is there no mention of the third son from that marriage, Swietopelk? Fourth, why is Cracow, which had been probably conquered by Mieszko earlier, mentioned as borderland, not as part of Shinesghe civitas? Fifth, why instead of the name Mieszko, he is addressed as Dagome, nowhere else he is called by that name (see Scandinavian connections to Mieszko I) These issues have been addressed by historians in many books and articles, and although there is some common agreement to most solutions (for example, the absence of Boleslaw can be explained by old Slavic custom, in which all children received their part of their heritage as soon as they matured, so Boleslaw could receive Cracow as his part of father's legacy) they are still open.
This is full text of Dagome Iudex in latin:
[1] There is no doubt today, that that name describes Mieszko I. Only controversion is: is this an incorrect writing of his name, or, as some (Łowmiański) think, his second, christian name (Dago, Dagon, Dagobert)
[2] Iudex in ancient Rome and in Bizantium (archon) meant someone who made work ordered by someone else, but sometimes it could also mean sovereign ruler. Princes of Slavic tribes were sometimes described by that name. Some suggest an error here in the writing and correct it to dux.
[3] In this context that means lady
[4] What's most controversial is in that document, is that Boleslaw I Chrobry, oldest son of Mieszko, is not mentioned, only sons from marriage with Ote.
[5] Some historians think this is mangled writing of Gniezno, capitol of Poland in that time, but some think this could be Szczecin as well.
[6] Some translate longum mare as long sea and some as Pomorze, but in 990 Pomorze was probably already within the borders of Poland, so more probably first translation is more correct.
[7] Alemure could mean some city, or Olomuniec, or Morawy.
[8] It seems that state of Gniezno was separate entity, and other parts of country were regions attached to it as, probably, conquered provinces.
NOTE: footnotes are summary of arguments from Labuda's book.