The Fenni are first mentioned by Cornelius Tacitus in Germania in 98 A.D. Their location is uncertain, due to the vagueness of Tacitus' account:"they (Venedi) overrun in their predatory excursions all the woody and mountainous tracts between the Peucini and the Fenni". The Greco-Roman geographer Ptolemy, who produced his Geographia in ca. 150 AD, mentions a people called the Phinnoi, generally believed to be synonymous with the Fenni. He locates them in two different areas: a northern group in northern Scandia (Scandinavia), then believed to be an island; and a southern group, apparently dwelling to the East of the upper Vistula river (SE Poland). It remains unclear what was the relationship between the two groups.
The next ancient mention of the Fenni/Finni is in the Getica of 6th-century chronicler Jordanes. In his description of the island of Scandza (Scandinavia), he mentions three groups with names similar to Ptolemy's Phinnoi, the Screrefennae, Finnaithae and mitissimi Finni ("softest Finns"). The Screrefennae are believed to mean the "skiing Finns" and are generally identified with Ptolemy's northern Phinnoi and today's Finns. The Finnaithae have been identified with the Finnveden of central Sweden. It is unclear who the Finni mitissimi were.
Tacitus was unsure whether to classify the Fenni as Germanic or Sarmatian. The vagueness of his account has left the identification of the Fenni open to a variety of theories. It has been suggested that the Romans may have used Fenni as a generic name, to denote the various non-Germanic (i.e., Balto-Slavic and Finno-Ugric) tribes of NE Europe. Against this argument is the fact that Tacitus distinguishes the Fenni from other probably non-Germanic peoples of the region, such as the Aestii and the Venedi.
It has also been suggested that Tacitus' Fenni could be the ancestors of the modern Finnish people. Juha Pentikäinen writes that Tacitus may well have been describing the Sami or the proto-Finns when referring to the Fenni, noting some archeologists have identified these people as indigenous to Scandinavia. The context of Fenni has also included the Finnic Estonians throughout different interpretations. Nevertheless, according to some linguists, certain linguistic evidence may be interpreted supporting the idea of an archaic Indo-European dialect and unknown Paleo-European languages existing in north-eastern Baltic Sea region before the spread of Finno-Ugric languages like Proto-Sami and Proto-Finnic in the early Bronze age around 1800 BC. However, during Tacitus days (1st century AD) Finno-Ugric languages (Proto-Sami and Proto-Finnic) were the main languages in the northern Fennoscandia. 
Another theory is that Tacitus' Fenni and Ptolemy's northern Phinnoi were the same people and constituted the original Sami people of northern Fennoscandia, making Tacitus' description the first historical record of them. But while this may seem a plausible identification for the Phinnoi of north Scandinavia, it is dubious for Tacitus' Fenni. Tacitus' Fenni (and Ptolemy's southern Phinnoi) were clearly based in continental Europe, not in the Scandinavian peninsula, and were thus outside the modern range of the Sami. Against this, there is some archaeological evidence that the Sami range may have been wider in antiquity. Sami toponyms are found as far as Southern Finland and Karelia 
The uncertainties have led some scholars to conclude that Tacitus' Fenni is a meaningless label, impossible to ascribe to any particular region or ethnic group. But Tacitus appears to relate the Fenni geographically to the Peucini and the Venedi, albeit imprecisely, stating that the latter habitually raided the "forests and mountains" between the other two. He also gives a relatively detailed description of the Fenni's lifestyle.
"In wonderful savageness live the nation of the Fenni, and in beastly poverty, destitute of arms, of horses, and of homes; their food, the common herbs; their apparel, skins; their bed, the earth; their only hope in their arrows, which for want of iron they point with bones. Their common support they have from the chase, women as well as men; for with these the former wander up and down, and crave a portion of the prey. Nor other shelter have they even for their babes, against the violence of tempests and ravening beasts, than to cover them with the branches of trees twisted together; this a reception for the old men, and hither resort the young. Such a condition they judge more happy than the painful occupation of cultivating the ground, than the labour of rearing houses, than the agitations of hope and fear attending the defense of their own property or the seizing that of others. Secure against the designs of men, secure against the malignity of the Gods, they have accomplished a thing of infinite difficulty; that to them nothing remains even to be wished."
This description is of a lifestyle much more primitive than that of the medieval Sami, who were pastoralists living off herds of reindeer and inhabiting sophisticated tents of deer-hide. But the archaeological evidence suggests that the proto-Sami and Proto-Finns had a lifestyle more akin to Tacitus' description.
- Tacitus G.46
- Mattingly (1970)
- Ptolemy II.11 and III.5
- Jordanes G.III)
- Olaus Magnus (1658) . "The Description of Scricfinnia". Historia de Gentibus Septentrionalibus. Rome.
- R. Bosi, The Lapps (1960) pp44-7
- Tacitus G.45-6
- Anderson (1958) 217
- Pirinen 9
- Juha Pentikäinen, Kalevala Mythology, Indiana University Press, 1999, p226
- Mikko Heikkilä: Bidrag till Fennoskandiens språkliga Förhistoria i tid och rum. University of Helsinki. 2014. tps://helda.helsinki.fi/bitstream/handle/10138/135714/bidragti.pdf - Abstract in English pp. 7-8
- Antte Aikio 2006: On Germanic-Saami contacts and Saami prehistory. http://www.sgr.fi/susa/91/aikio.pdf
- Tägil (1995) 118
- Kinsten (2000)
- Doug Simms, The University of Texas, The Early Period of Sámi History, from the Beginnings to the 16th Century
- Whitaker (1980)
- Hansen & Olsen (2004)
- Ante Aikio 2007: The study of Saami substrate toponyms in Finland. Onomastica Uralica. http://mnytud.arts.klte.hu/onomural/kotetek/ou4/08aikio.pdf
- Whitaker (1963)
- Svensk Etymologisk Ordbok (online)
- Anderson, J.G.D. (1958) Textual note to Tacitus' Germania
- Bosi, Roberto (1960): The Lapps
- Hansen, L.I. & Olsen, B. (2004): Samenes Historie fram til 1750
- Kinsten, Silje Bergum (2000): "The Northern Sami People" (The Norway Post, 19 August 2000)
- Pirinen, Kauko The settlement of Finland begins in Eino Jutikkala (ed.) A History of Finland (trans. Paul Sjoblom)
- Tägil, Sven (1995): Ethnicity and nation building in the Nordic world, ISBN 1-85065-239-2