diff --git a/src/app.rs b/src/app.rs
index 4f12e25..5260a5f 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -4,14 +4,15 @@ use bomper::{
     config::Config,
     error::{Error, Result},
     replacers::{
-        cargo::CargoReplacer, search::SearchReplacer, simple::SimpleReplacer, Replacer,
-        VersionReplacement,
+        cargo::CargoReplacer, file::FileReplacer, search::SearchReplacer, simple::SimpleReplacer,
+        Replacer, VersionReplacement,
     },
     versioning::{
         determine_increment, get_commits_since_tag, get_latest_tag, increment_version,
         VersionIncrement,
     },
 };
+use std::io::Write;
 
 pub struct App {
     pub args: BaseArgs,
@@ -55,66 +56,126 @@ impl App {
             _ => unreachable!(),
         };
         let new_version = increment_version(tag.version.clone(), increment);
-        println!("New version: {}", new_version);
         let changelog_entry = generate_changelog_entry(&commits, &new_version);
-        println!("{}", changelog_entry);
-        todo!()
+
+        let replacement = VersionReplacement {
+            old_version: tag.version.to_string(),
+            new_version: new_version.to_string(),
+        };
+        let mut file_changes = determine_changes(&self.config, &replacement)?;
+        file_changes.push(apply_changelog(changelog_entry)?);
+        apply_changes(file_changes, &self.args)?;
+
+        Ok(())
     }
 
     pub fn raw_bump(&self, opts: &RawBump) -> Result<()> {
-        // self.config.file.clone().par_drain().for_each(|path| {
-        let versions = VersionReplacement {
+        let replacement = VersionReplacement {
             old_version: opts.old_version.clone(),
             new_version: opts.new_version.clone(),
         };
-        let mut files_to_replace = Vec::new();
-
-        let by_file = &self.config.by_file;
-        if let Some(by_file) = by_file {
-            for (path, config) in by_file {
-                let mut replacers = match &config.search_value {
-                    Some(value) => SearchReplacer::new(
-                        path.clone(),
-                        &opts.old_version,
-                        value,
-                        &opts.new_version,
-                    )?
-                    .determine_replacements()?,
-                    None => {
-                        SimpleReplacer::new(path.clone(), &opts.old_version, &opts.new_version)?
-                            .determine_replacements()?
-                    }
-                };
-
-                // append new replacers to the list
-                if let Some(replacers) = &mut replacers {
-                    files_to_replace.append(replacers);
-                }
-            }
+        let file_changes = determine_changes(&self.config, &replacement)?;
+        apply_changes(file_changes, &self.args)?;
+
+        Ok(())
+    }
+}
+
+/// Persist file changes to the filesystem.
+/// This function is responsible for respecting the `dry_run` flag, so it will only persist changes
+/// if the flag is not set.
+fn apply_changes(changes: Vec<FileReplacer>, args: &BaseArgs) -> Result<()> {
+    if args.dry_run {
+        println!("Dry run, not persisting changes");
+        for replacer in changes {
+            println!("Would have replaced: {}", replacer.path.display());
         }
 
-        let cargo_lock = &self.config.cargo;
-        if let Some(cargo_lock) = cargo_lock {
-            let replacer = CargoReplacer::new(versions, cargo_lock.clone())?;
-            let mut files = replacer.determine_replacements()?;
-            if let Some(files) = &mut files {
-                files_to_replace.append(files);
-            }
+        return Ok(());
+    } else {
+        for replacer in changes {
+            replacer.persist()?;
         }
+    }
 
-        if self.args.dry_run {
-            println!("Dry run, not persisting changes");
-            for replacer in files_to_replace {
-                println!("Would have replaced: {}", replacer.path.display());
-            }
+    Ok(())
+}
+
+/// Determine the changes to make to the repository to update the version.
+fn determine_changes(
+    config: &Config,
+    replacement: &VersionReplacement,
+) -> Result<Vec<FileReplacer>> {
+    let mut files_to_replace = Vec::new();
 
-            return Ok(());
-        } else {
-            for replacer in files_to_replace {
-                replacer.persist()?;
+    let by_file = &config.by_file;
+    if let Some(by_file) = by_file {
+        for (path, config) in by_file {
+            let mut replacers = match &config.search_value {
+                Some(value) => SearchReplacer::new(
+                    path.clone(),
+                    &replacement.old_version,
+                    value,
+                    &replacement.new_version,
+                )?
+                .determine_replacements()?,
+                None => SimpleReplacer::new(
+                    path.clone(),
+                    &replacement.old_version,
+                    &replacement.new_version,
+                )?
+                .determine_replacements()?,
+            };
+
+            // append new replacers to the list
+            if let Some(replacers) = &mut replacers {
+                files_to_replace.append(replacers);
             }
         }
+    }
 
-        Ok(())
+    let cargo_lock = &config.cargo;
+    if let Some(cargo_lock) = cargo_lock {
+        let replacer = CargoReplacer::new(replacement.clone(), cargo_lock.clone())?;
+        let mut files = replacer.determine_replacements()?;
+        if let Some(files) = &mut files {
+            files_to_replace.append(files);
+        }
     }
+
+    Ok(files_to_replace)
+}
+
+/// Stitch together the existing changelog with the new one.
+/// This is done using `- - -` as a marker character.
+/// The new changelog is composed of the changelog header (everything from the start to the first
+/// marker`, the new entry (with a marker on top), and the remaining part of the previous changelog
+fn create_changelog(path: &std::path::Path, contents: &str) -> Result<String> {
+    const MARKER: &str = "- - -";
+
+    match std::path::Path::try_exists(path) {
+        Ok(true) => {
+            let original_changelog = std::fs::read_to_string(path)?;
+            let start = original_changelog
+                .find(MARKER)
+                .ok_or(Error::ChangelogMarker)?;
+
+            let header = &original_changelog[..start];
+            let rest = &original_changelog[start..];
+            Ok(format!("{header}\n{MARKER}\n{contents}\n{rest}"))
+        }
+        Ok(false) => Ok(format!("# Changelog\n\n{MARKER}\n{contents}")),
+        Err(e) => Err(e.into()),
+    }
+}
+
+fn apply_changelog(entry: String) -> Result<FileReplacer> {
+    let path = std::path::PathBuf::from("CHANGELOG.md");
+    let new_changelog = create_changelog(&path, &entry)?;
+
+    let temp_file = tempfile::NamedTempFile::new_in(".")?;
+    let mut file = temp_file.as_file();
+    file.write_all(new_changelog.as_bytes())?;
+
+    Ok(FileReplacer { path, temp_file })
 }
diff --git a/src/error.rs b/src/error.rs
index d9e3a60..a850b96 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -49,6 +49,8 @@ pub enum Error {
     ProjectBaseDirectory,
     #[error("unable to determine the most recent tag")]
     TagError,
+    #[error("changelog does not contain marker character")]
+    ChangelogMarker,
 }
 
 impl std::fmt::Debug for Error {
diff --git a/src/replacers/mod.rs b/src/replacers/mod.rs
index 784d0ee..9617506 100644
--- a/src/replacers/mod.rs
+++ b/src/replacers/mod.rs
@@ -11,6 +11,7 @@ pub trait Replacer {
     fn determine_replacements(self) -> Result<Option<Vec<FileReplacer>>>;
 }
 
+#[derive(Clone, Debug)]
 pub struct VersionReplacement {
     pub old_version: String,
     pub new_version: String,