labour mobility

As shown on the diagram there are an estimated 169 million people who are classified as a migrant worker.
This accounts for almost 5% of the total global workforce.
99 million are male / 70 million are female.
The majority of workers are employed in the service sector.
Many of these workers are temporary or semi-permanent workers, who intent to return home in the future.
In some countries (particularly Middle Eastern nations) migrants make up a significant percentage of the labour force.
In the European Union free movement of people allows anyone to move to any country within the bloc for work.
Elsewhere there are significant barriers to labour mobility leading to high percentages of migrants in undocumented workers in informal work.
Migrant workers may be subjected to discrimination in the country they work - the Qatar World Cup has highlighted the significant issues faced by migrant workers in the country.

positives for host country

Supply of cheap labour in construction and the service sector e.g. security/cleaning/retail.
Migrants fill shortages in sectors such as the health service.
Migrants pay taxes in the host country which contributes towards government spending on public services.

negatives for host country

Perception that foreign workers take jobs away from local workers.
Wage suppression in some sectors as foreign workers accept lower wages and longer hours than local workers.
Increased demand on housing and infrastructure.

positives for source country

Less burden on services such as healthcare/housing.
Remittances - money sent home by workers is spent by their families in the local economy.

negatives for source country

Brain drain - the loss of skilled workers to other countries can lead to decline of public services.
Loss of tax revenue as workers pay taxes in the host country.