Business, economics, and international relations are traditionally popular choices.
That makes sense in Spain. The country is home to international companies, banks, consulting firms, and technology projects. In larger cities, students can also find internship opportunities while they are still studying.
Interest in digital fields is growing quickly. Popular choices include Computer Science, Data Science, artificial intelligence, cybersecurity, and engineering.
Medicine, dentistry, and physiotherapy also remain popular, although admission is usually much more competitive.
Spain also offers strong programs in architecture, design, communications, tourism, and marketing.
The language of instruction is something worth checking twice.
The fact that you are studying in Spain does not mean every lecture will be in Spanish. Some degrees are taught entirely in English. In Catalonia, certain subjects may be taught in Catalan. Sometimes even one degree includes courses taught in different languages.
It is much better to know this before arriving than to discover it in September.