Latvians, together with the Lithuanians, are the only nations speaking Baltic languages left in the world. Their relations are generally very good, and they call each other brothers. While there have been some political downtimes this has never made Lithuanians and Latvians dislike each other.
There are only some 3 000 Latvians in Lithuania however - much less than there are either Poles, Russians or Belarussians. One part of Latvians lives in historical communities in the northern Lithuania close to the border of Latvia. Another part of Lithuania's Latvians lives in the major cities where they have largely immigrated in 1940s and later from Latvia-proper.
In 1918 when both Lithuania and Latvia became independent from the Russian empire the ethnic boundary was far more dilluted. There was a short dispute on where the Lithuanian-Latvian border should run, solved by a peaceful arbitration in 1922. Still the new border left many people "on the wrong side", with some northern Lithuanian towns (e.g. Palanga) being 10%-25% Latvian. Overally there were 14 883 Latvians in Lithuania according to the 1923 census (0,7% of the entire Lithuanian population).
There were always significantly more Lithuanians in Latvia than there were Latvians in Lithuania however, both in the borderland and in the major cities.
Subsequently the minorities on both sides of the border decreased due to various reasons, not the least among them emigration to their newly-established ethnic homeland. The Soviet population transfers failed to replenish the communities.
Latvian nation is multi-religious with strong Roman Catholic and Lutheran communities. Latvians of Lithuania were traditionally overwhelmingly Lutheran (in 1923 as much as 91% of Lithuania's Latvians were Lutheran). Today however only 36% of Lithuania's Latvians are Lutheran, another 36% are Roman Catholic and some 21% are irreligious (as per 2001 census).
Perhaps because their cultural similarity to Lithuanians the Latvians of Lithuania generally receive less public attention than other traditional minorities of comparable size.