A UK judgement
If you have a judgement for payment of money from another part of the UK then the process is relatively simple. The solicitors dealing with the original action in, for example, England would ask the English court to grant a Certificate of Money Provisions under the Civil Jurisdiction and Judgements Act 1982 and we would then register that certificate in the Books of Council and Session. The registered certificate would have the same effect as a Scottish court decree and you would then be able to enforce that decree in the usual way.
If the judgement from another part of the UK is not for payment of money then things become slightly more complicated. Rather than simply registering a certificate in Scotland we would have to Petition the Court of Session in Edinburgh in order to have the judgement registered. In practice, that is likely to be a formality as most of the defences that are relevant would have already been explored in depth in the originating court. However, it is a more formal and expensive process.
An EU judgement
If the Judgement is not from another part of the UK but rather from another EU Member State then the position is not much more complicated. EC Council Regulation 44/2001 provides that "A judgement given in a Member State shall be recognised in other Member States without any special procedure being required". So, the only procedure that is required is very similar to the procedure for non-money judgements within the UK. A Petition is presented to the Court of Session seeking registration of the EU Judgement.
A non-EU judgement
If the judgement to be registered is from a court outwith the EU then the ease with which it can be registered will depend on where the judgement is from. The Administration of Justice Act 1920 and the Foreign Judgements (Reciprocal Enforcement) Act 1933 each contain provisions which provide for the reciprocal enforcement of judgements with Scotland. The countries to which these apply are primarily (but not exclusively) Commonwealth countries and if the country is on the list then, as above, a Petition can be presented to the Court of Session seeking registration of that judgement in Scotland.
There are some countries, however, which do not have reciprocal arrangements with Scotland. The most notable perhaps being the USA. In that case, the procedure is different again and more difficult. Rather than simply lodging a Petition you would have to raise an action of Decree Conform which is in the form of a Summons and is a more expensive process. Basically, the Summons would seek payment of whatever sum was due by the debtor in the originating court and ask the Court of Session to grant a decree for payment in Scotland.
Hopefully that provides a useful overview of the provisions for registration of judgements in Scotland. The complexity and expense of registration will depend on where the originating court is and what sort of judgement you are seeking to register. You may, of course, be on the other side of the equation and be looking to oppose registration and enforcement in Scotland. That is entirely possible but the issues involved again depend primarily on what sort of registration we are talking about. If it is the registration of an English money judgement then there is little chance for opposition other than at the enforcement stage. If it is a Petition based on a judgement from the UK or EU then any Answers tend to be directed to procedural irregularities (e.g. such as there not being a final judgement in the originating court). If it is a Petition on the basis of a judgement from outwith the EU or an action of Decree Conform then issues like public policy and natural justice can come into play more regularly. In any case, however, opposition to registration is not an easy fight to win.