Military recruiting during the Thirty Years War was largely done by private contractors. Rulers signed a contract with a colonel specifying the number of soldiers to be provided, duration and location of service, etc. The colonel was then responsible for levying the required men, providing them with weapons and supplies, and transporting them to the intended destination. Contracts with foreign rulers did sometimes include some reimbursement for these expenses or made arrangements for transportation or victualing. Permits to recruit in an area were issued by local governments and usually had strict stipulations on the number and ages of potential recruits.

I will address the specific case of Scotland in a moment, but first a bit of background on Europe as a whole. On the continent military recruiting was highly commercialized. Entrepreneurial colonel-proprietors engaged in highly speculative investment schemes that could be extremely financially lucrative. Essentially the regiment was run as a private business for the colonel's profit. As many costs as possible were either covered in the service contract with a foreign ruler or were passed down to the soldiers themselves. Equipment, food, and clothing were all sold above cost to the rank and file, usually paid for by salary deductions rather than directly purchased by the soldiers. In fact many contractors were owners or investors in private factories for the production of weapons and armor. Such direct access further reduced costs. Colonel-proprietors also could increase their profit margins using other less-than-legal mechanisms like failing to report casualties and pocketing the dead soldiers' salaries, a practice called "dead-pays".

All of these strategies were used to offset the enormous costs of recruiting, equipping, and maintaining an early modern army regiment. As states often did not have the ready cash to directly hire and equip massive armies, as much of the financial burden as possible was shifted to the colonel-proprietors. It was a volatile market. Large risks could be rewarded with large returns, but unsuccessful colonels could easily find themselves bankrupt or heavily in debt.

Not all recruiters operated in such a speculative fashion, however. Colonels of Swiss or Scottish origin, for example, were often hesitant to involve themselves in capital-intensive personal investments. They refused to engage in speculative recruiting or to invest their personal fortunes, only beginning their enterprise after an up-front cash payment from the ruler. This more conservative approach meant that Scottish colonels were less likely to amass huge fortunes but their enterprises were accordingly less likely to result in failure or bankruptcy.

If you were a Scottish mercenary, you would have been recruited by a private Scottish colonel-contractor that had been awarded a recruiting permit in your local area. The colonel would have also previously signed a contract with a foreign ruler for the regiment's service--in Scotland's case the most likely foreign employers during the Thirty Years War were Sweden, Denmark, and France. You would be recruited alongside others as part of a single regiment. Some wealthy colonels could raise multiple regiments at a time, but this was less common, and usually recruiters were dispersed to different areas so as not to compete with one another.

There were few requirements for recruitment--you must of course be able-bodied and willing to submit to harsh discipline, but otherwise there were not many restrictions on recruits. Age was one; the permitted range was usually set by the local government and though it changed over time was usually around ages 20-40. Prior experience or even a clean criminal record was not required. In fact prisons were a lucrative source of recruits--punishments for petty crimes like stealing and assault could be absolved in exchange for enlisting.

The new regiment would be equipped by the colonel-contractor, but the cost of any weapons or equipment you received would be docked from future pay. Together the regiment was transported to the intended destination. While on campaign it was unlikely that you would actually receive your promised salary in anything approaching regular payments, and under a particularly capricious colonel your cost of living may at times cancel out any potential earnings. Food, clothing, and replacements for broken equipment were all deducted from your salary. Your service ended after the specified time, when the ruler terminated the contract, or you were wounded, killed, or captured.

If you survived you stood a chance of becoming a sergeant or NCO, who sometimes earned double the salary of a green recruit. Some NCOs shared in the profits of the regiment, and in this way it was possible to earn a significant revenue from army service, but most often soldiers made very little money over the course of their careers.

Parrott, David. The Business of War: Military Enterprise and Military Revolution in Early Modern Europe, Cambridge: Cambridge University Press, 2012.