Fundamental Factors

In economics, inflation is a rise in the general level of prices of goods and services in an economy over a period of time. The term "inflation" once referred to increases in the money supply (monetary inflation); however, economic debates about the relationship between money supply and price levels have led to its primary use today in describing price inflation. Inflation can also be described as a decline in the real value of money—a loss of purchasing power in the medium of exchange which is also the monetary unit of account. When the general price level rises, each unit of currency buys fewer goods and services. A chief measure of price inflation is the inflation rate, which is the percentage change in a price index over time.
Inflation can cause adverse effects on the economy. For example, uncertainty about future inflation may discourage investment and saving. High inflation may lead to shortages of goods if consumers begin hoarding out of concern that prices will increase in the future.
Economists generally agree that high rates of inflation and hyperinflation are caused by an excessive growth of the money supply. Views on which factors determine low to moderate rates of inflation are more varied. Low or moderate inflation may be attributed to fluctuations in real demand for goods and services, or changes in available supplies such as during scarcities, as well as to growth in the money supply. However, the consensus view is that a long sustained period of inflation is caused by money supply growing faster than the rate of economic growth.
Today, most economists favor a low steady rate of inflation. Low (as opposed to zero or negative) inflation may reduce the severity of economic recessions by enabling the labor market to adjust more quickly in a downturn, and reducing the risk that a liquidity trap prevents monetary policy from stabilizing the economy. The task of keeping the rate of inflation low and stable is usually given to monetary authorities. Generally, these monetary authorities are the central banks that control the size of the money supply through the setting of interest rates, through open market operations, and through the setting of banking reserve requirements.

Interest Rate

An interest rate is the price a borrower pays for the use of money they do not own, for instance a small company might borrow from a bank to kick start their business, and the return a lender receives for deferring the use of funds, by lending it to the borrower. Interest rates are normally expressed as a percentage rate over the period of one year.
Interest rates targets are also a vital tool of monetary policy and are used to control variables like investment, inflation, and unemployment.

Unemployment Rate

Unemployment occurs when a person is available to work and currently seeking work, but the person is without work. The prevalence of unemployment is usually measured using the unemployment rate, which is defined as the percentage of those in the labor force who are unemployed. The unemployment rate is also used in economic studies and economic indexes such as the United States' Conference Board's Index of Leading Indicators as a measure of the state of the macroeconomics.
There are a variety of different causes of unemployment, and disagreement on which causes are most important. Different schools of economic thought suggest different policies to address unemployment. Monetarists for example, believe that controlling inflation to facilitate growth and investment is more important, and will lead to increased employment in the long run. Keynesians on the other hand emphasize the smoothing out of business cycles by manipulating aggregate demand. There is also disagreement on how exactly to measure unemployment. Different countries experience different levels of unemployment; the USA currently experiences lower unemployment levels than the European Union, and it also changes over time (e.g. the Great depression) throughout economic cycles.

Monetary Policy

Monetary policy is the process by which the government, central bank, or monetary authority of a country controls the supply of money, availability of money, and cost of money or rate of interest, in order to attain a set of objectives oriented towards the growth and stability of the economy. Monetary theory provides insight into how to craft optimal monetary policy.
Monetary policy is referred to as either being an expansionary policy, or a contractionary policy, where an expansionary policy increases the total supply of money in the economy, and a contractionary policy decreases the total money supply. Expansionary policy is traditionally used to combat unemployment in a recession by lowering interest rates, while contractionary policy involves raising interest rates in order to combat inflation. Monetary policy should be contrasted with fiscal policy, which refers to government borrowing, spending and taxation.

There are many more fundamental factors but the most important are those which I described in this article.
Thanks to Wikipedia