Capital flows encompass all of the money moving between countries as a result of investment flows into and out of countries around the world. Here instead of money flowing between countries to buy each others goods and services, we are talking about money flowing into and out of the stock and bond markets of countries around the world, as well as things such as real estate and cross boarder mergers and acquisitions.
Just as the importing or exporting of goods shifts the supply demand balance for a particular country, so do the flows of money coming into and out of the country as a result of capital flows. As the barriers to investing in foreign countries have come down as a result of the internet and other factors, it is much easier for fund managers and other investors to take advantage of opportunities not only in their domestic markets, but anywhere in the world. As this is the case, when a market in a particular country is showing above average returns, foreign investors will often flood the market with capital, buying up the assets of that country looking to earn above average returns as well. When this happens it not only affects the markets of that country, but also the value of its currency, as foreign capital must be converted into local currency in order to participate in the markets there.
While most people are more familiar with the equities markets, an important thing to note here is that the bond markets in most countries are much larger than the equities markets, and therefore can have a greater affect on the currency. When the interest rates being paid for the bonds in a particular country are high, this tends to attract capital to that country from foreign investors seeking to take advantage of that higher yield, creating a demand for the local currency here as well.
Lastly, cross boarder mergers and acquisitions are also part of the capital flows category and when they happen on large levels can move the market as well. As an example, if Deutsche bank (a large German bank) were to buy Washington Mutual here in the United States, this would create a large demand for dollars and increase the supply of Euros on the market as Deutsche Bank sold Euros for dollars in order to complete the transaction.
As you can probably imagine there are a myriad of factors that can affect both trade and capital flows for a particular country, and therefore its currency. As currency traders it is our responsibility to know what to expect in terms of a reaction in the FX market when different things happen, so always think of things in terms of how something effects the supply demand relationship. Once you understand this it is next important to understand whether that effect fits into the trade flow or capital flow category since, as we will learn in later lessons, some countries are affected more by trade flows than capital flows and vice versa.