The number of files received by the Director of Public Prosecutions (DPP) has more than doubled in the past five years, reaching a record 15,214 files last year.
The vast majority of these related to the investigation of crime, according to the DPP's 2006 annual report.
When gardaí complete an investigation, they send a file to the DPP, who then decides if a prosecution should be taken and, if so, what the charges should be.
The DPP, James Hamilton, said his caseload had increased on a year-on-year basis, "both in terms of the number of files received and the complexity of the issues that have to be addressed".
His directing division decided against a prosecution in 35 per cent of cases last year.
Insufficient evidence was the reason given in almost 80 per cent of these cases. Other reasons included the fact that the suspect had become involved in the juvenile diversion programme; the time limit had expired; or the suspect had died or disappeared.
While some victims or their families have complained about the length of time taken by the DPP to decide on a prosecution, the report shows that, in 2006, more than half of directions were made in less than two weeks. A decision was taken within six months in 93 per cent of cases.
In 41 cases last year, Mr Hamilton's office lodged an appeal for a review of the sentence on the grounds of leniency. This was almost a doubling of the number of appeals when compared with 2004.
However, the vast majority of the appeals heard last year were unsuccessful. Some 50 appeals on the grounds of leniency were heard last year and 33 of these were refused.
The report also highlights the increasing number of requests received under the European Arrest Warrant Act since it was introduced in 2004.
To return a suspect to the State to investigate a crime, gardaí must apply for an extradition warrant from the DPP's office.
While the Garda's extradition unit made 13 extradition requests in 2004, this had risen to 40 by last year.
"If the numbers increase, as they have done, the challenge in the future for the office will be to be prepared to deal effectively with the increased volume of files," the report states.
It adds: "Arrangements have already been put in place in the office to deal with the potential increase in European arrest warrant files."
Mr Hamilton said the European arrest warrant was "proving to be a very effective instrument in securing the return of accused persons".
He pointed out that just one country had refused to hand over a suspect to the State since 2004, but that case was unique for a number of reasons.
