What are the requirements for obtaining a visa to enter Thailand?

Don't think it's changed since you asked on 10 April

In my experience, nearly the entire visa application process is online. You require a decent connection to upload photos and complete several pages of questions.

I have just submitted my passport to the Thai embassy in Madrid after extensive procurement of necessary documents.

It is a long and expensive process to achieve all the necessary requirements for a visa.

The reason you enter Thailand determines the type of visa you will need. I am guess by the question you will require a tourist visa. The requirements for tourist visa vary depending on passport (nationality). Tourist visa are short lived (60 days or 90 days or something, depends on your nationality). If you are looking to stay longer (years) then you will look for long term visa, those are generally "Non B" or 'Non O' visas. They are issued for: retirement, dependent, work, marriage. The other long term option is the elite visa which starts at/about $15,000 for 5 years.

Good luck

Correction and explanation. "Non B" stand for "Non Immigrant type B" and "Non O" stands for "Non Immigration Type O". The B visa (Non B ) is for business related activities (work Investment etc). The Non O is for something else which includes retirement and marriage... I am less familiar with the Type O, and not currently familiar with a Type B (I may actually be on Non B, but the agent worked it for me so I am pretty clueless).

The larger point is "Non-XXXXX" Is not like it sounds.. It is actually "Non Immigration Type XXXXX"

Why do you want to enter Thailand?