Different rules about residence and work in Estonia apply to citizens of the EU and to citizens of third countries. The length of your stay also influences which rules you have to follow.
EU citizens are free to enter Estonia, but if they stay for more than 3 months, they should register their place of residence and apply for an ID-card.
Citizens of third countries may need a visa for short-term visits (up to 6 months). Citizens of third countries need a residence permit for employment for long term work (more than 6 months) in Estonia.
Applications for visas, residence permits or residence permits for employment should be submitted to a diplomatic representation of the Republic of Estonia. Registration of one’s place of residence is necessary in the case of longer visits for EU citizens as well as citizens of third countries.